A shift position detecting device comprises a shift position sensor that continuously issues an output data that represents a shift position of the gear selection mechanism; and a control unit. The control unit includes a first shifting load instruction section that controls the shift actuator to shift the gear selection mechanism to the shift gear-in establishing position with a first shifting load; a second shifting load instruction section that, after completion of shifting of the gear selection mechanism to the shift gear-in establishing position by the first shifting load instruction section, controls the shift actuator to reduce the shifting load from the first shifting load to a second shifting load which is lower than the first shifting load; and a shift gear-in establishing position memory section that stores an output data issued from the shift position sensor when the shift actuator is controlled by the second shifting load instruction section, as an information data that represents completion of shifting of the gear selection mechanism to the shift gear-in establishing position.