This paper will present my own contribution to this subject. I believe the micro foundation of Keynesian macroeconomics exists in the context of Keynes's multiplier principle. Specifically, Keynes's multiplier analysis can also be viewed as a description of the process through which market exchanges are generated. This consideration provides us a new theoretical framework The way an economy operates is completely different from the way described by trad itional equilibrium analysis. Even the concept of equilibrium has to be changed. Yet the new theoretical framework provided here turns out to be much superior in the sense that many mysteries of trad itional microeconomics automatically disappear and further, the Keynesian macroeconomic relation is exactly specified in a micro economic context The paper is organized as follows. First, I will raise an issue, which I believe has long been suppressed in economic literature. This issue is crucial, for the theoretical framework of trad itional equilibrium analy incorrectly founded once this issue is concerned. My own contribution, however, is exactly generated from my attempt to deal with this issue. I then expose how Keynes's multiplier analysis can be understood as an approach to describe the generation process of market exchanges. There are two ways of this exposition: one I call the forward exposition and the other the backward exposition. Then two possible doubts will be addressed which seem to be, in the view of many economists, unsatisfactory to the multiplier theory. A mathematical model will follow to show how Keynesian macroeconomic relation can be specified in my micro model of market exchange. Finally, the relation between this multiplier approach to other approaches on this subject will be discussed Il. Demand and Supply, which one is the first? Consider an agent who comes to an economy. He certainly wants to have two types of exchange: buying and selling. Which one should he have first? The trad itional equilibrium analysis does not offer an explicit answer. Implicitly, the system assumes that agents make their3 This paper will present my own contribution to this subject. I believe the micro foundation of Keynesian macroeconomics exists in the context of Keynes's multiplier principle. Specifically, Keynes's multiplier analysis can also be viewed as a description of the process through which market exchanges are generated. This consideration provides us a new theoretical framework. The way an economy operates is completely different from the way described by traditional equilibrium analysis. Even the concept of equilibrium has to be changed. Yet the new theoretical framework provided here turns out to be much superior in the sense that many mysteries of traditional microeconomics automatically disappear and further, the Keynesian macroeconomic relation is exactly specified in a micro economic context. The paper is organized as follows. First, I will raise an issue, which I believe has long been suppressed in economic literature. This issue is crucial, for the theoretical framework of traditional equilibrium analysis is incorrectly founded once this issue is concerned. My own contribution, however, is exactly generated from my attempt to deal with this issue. I then expose how Keynes's multiplier analysis can be understood as an approach to describe the generation process of market exchanges. There are two ways of this exposition: one I call the forward exposition and the other the backward exposition. Then two possible doubts will be addressed, which seem to be, in the view of many economists, unsatisfactory to the multiplier theory. A mathematical model will follow to show how Keynesian macroeconomic relation can be specified in my micro model of market exchange. Finally, the relation between this multiplier approach to other approaches on this subject will be discussed. II. Demand and Supply, Which One is the First? Consider an agent who comes to an economy. He certainly wants to have two types of exchange: buying and selling. Which one should he have first? The traditional equilibrium analysis does not offer an explicit answer. Implicitly, the system assumes that agents make their