A control device (10) includes: target deceleration calculation means (101) for calculating a target deceleration by using a target deceleration map in which a target deceleration is set for each vehicle speed; command power-generation torque calculation means (102) for calculating a command power-generation torque based on the target deceleration, a rotation speed of a power generator (2), and a transmission gear ratio of a transmission (3); and command Duty calculation means (103) for calculating a command Duty based on the command power-generation torque, and the rotation speed and an output voltage of the power generator (2). The target deceleration map is calculated based on a vehicle-speed shift in accordance with actual running conditions when a vehicle is decelerating with fuel stop.