An assist device for use in an electric vehicle capable of allowing a driver to walk the electric vehicle in power assistance at an extremely slow speed, preventing a sudden start of the vehicle, allowing the driver to monitor an insufficient capacity of a storage battery even with the main switch of the vehicle turned off, and determining an accurate charge capacity by eliminating the surface charge state of the storage battery when a charging operation ends. According to the present invention, firstly, the running motor of the vehicle is shifted to an extremely slow speed mode when the driver's dismounting is sensed and when the closed state of an accelerator is sensed. Secondly, a sudden start is prevented when the main switch is turned on with the accelerator opened. Thirdly, the reverse rotary motion of the running motor is transmitted to a stand mechanism via a one-way clutch. Fourthly, the operation of both a remaining capacity meter and insufficient capacity alarm means are continuously operated for a predetermined of time after turn-off of the main switch by means of timer means that is activated by the turn-off of the main switch when the storage battery suffers an insufficient capacity. Fifthly, the capacity of the storage battery is determined after the surface charge of the storage battery is eliminated when a charging operation is complete.