This is a second paper of a series of macroeconomic modeling that tries to model macroeconomic dynamics such as the determination of GDP (Gross Domestic Product) and money supply from system dynamics perspective. Following the first paper on the money supply and creation of deposits, this second paper tries to model dynamic determination processes of GDP, interest rate and price level on the same basis of the principle of accounting system dynamics developed by the author. For this purpose, a simple Keynesian multiplier model is constructed as a base model to examine a dynamic determination process of GDP. It is then expanded to incorporate the interest rate, whose introduction enables the analysis of aggregate demand equilibria as well as transactions of savings and deposits, and government debt and securities. Finally, a flexible price is introduced to adjust an interplay between aggregate demand equilibrium and full capacity output level. A somewhat surprise result of business cycle is observed from the analysis.