A shift actuator comprises a drive shaft and a housing that rotatably supports the drive shaft. A shift position detecting apparatus detects a rotational position of the drive shaft. The drive shaft is connected to a shift mechanism by an operating lever and a shift rod. The operating lever and the housing are respectively formed with a through hole and a bottomed hole. The drive shaft can be temporarily secured in rotational position by inserting a lever positioning pin into the through hole and the bottomed hole. When secured, the shift position detecting apparatus can be attached to the housing and a length of the shift rod can be adjusted.