1. A numerical analysis method of a vehicle drive unit that is provided with a moving body that moves inside a case and a cooling medium that is a fluid that fills a portion of the inside of the case and contacts at least a portion of the moving body, and in which the temperature of the fluid medium rises as the moving body continues to move, the numerical analysis method numerically analyzing a temperature field of the cooling medium and a flow field of the cooling medium, comprising: a first analyzing step, performed by an electronic calculator, that conducts numerical analysis of the flow field but does not conduct numerical analysis of the temperature field in a moving state in which the moving body is moving; a second analyzing step, performed by an electronic calculator, that conducts both numerical analysis of the flow field and numerical analysis of the temperature field in the moving state, after the first analyzing step ends; a third analyzing step, performed by an electronic calculator, that conducts numerical analysis of the temperature field but does not conduct numerical analysis of the flow field in the moving state, after the second analyzing step ends; and a fourth analyzing step, performed by an electronic calculator, that conducts both numerical analysis of the flow field and numerical analysis of the temperature field in the moving state, after the third analyzing step ends, wherein the first analyzing step and the second analyzing step are alternately executed at a preset operating ratio in which the number of operations of the first analyzing step is greater than the number of operations of the second analyzing step; and when the flow field reaches a steady state in the first analyzing step or the second analyzing step, the first analyzing step or the second analyzing step ends and the third analyzing step begins.