To provide a power generation system for a vehicle capable of controlling a power generation state while taking account of both the charging state of a battery and power generation efficiency.

The power generation system for the vehicle comprises a generator 20 for the vehicle rotary-driven by an engine 10, and a rotation number variable unit 30 for transmitting torque generated from the engine 10 to the generator 20 for the vehicle such that the r.p.m. of the generator 20 for the vehicle falls within any one of a relatively high first rotation number region or a relatively low second rotation number region. An ECU 60 controls a speed increase ratio of the rotation number variable unit 30 based on the traveling state of the vehicle and the charged state of a battery 50 thus controlling the rotation number of the generator 20 for the vehicle to fall within the first rotation number region or the second rotation number region.