To provide a select assist device for an automatic transmission having an increased degree of freedom of layout with a smaller size of select lever and select lever operating force property as requested while securing reliability by mechanically connecting the select lever to a range position changing device.

A failure determining block 50 is provided for determining a failure when an operation position detected by a potentiometer 25 is not displaced at fixed time intervals in the state that the displacement of input operating force is detected by a torque sensor 21.