A motor control device for controlling an electric motor (1,6) installed in a vehicle, is disclosed. The motor has a field winding (101,601). The motor control device has a battery (4) charged by power at a first voltage (Vb), an voltage increase/decrease inverter (3) capable of increasing the first voltage from the battery, an excitation control circuit (102, 106) which allows or disallows supply of the exciting current to the field winding (101,601), a sensor (35,41 48) which detects a state of the vehicle, and a controller (8). The controller (8) determines whether or not to start the motor (1,6) based on a signal from the sensor (41 48). When the motor is to be started, the controller (8) allows supply of exciting current by the excitation control circuit (102, 106) and controls the voltage increasing circuit so that the first voltage is increased to a second voltage higher than the first voltage (Vb).