To provide a select assisting device of an automatic transmission capable of changing a range at fail by mechanical connection between a select lever and a range position changing device, improving flexibility in layout thanks to miniaturization of the select lever, and providing the operation force characteristics for the selector lever that is based on requirement.

A control unit 22 comprises a protection circuit part 55 for judging whether a calculated drive signal is outputted correctly or not, a gate drive circuit part 59 which switches to energize an assisting actuator 9 only when the calculated drive signal is correctly outputted, and a transistor 62.