A coupling plate of a detent lever is assembled to an oil-pressure control device, wherein a transmission casing is a base for an assembling process. A slider of a range sensor coupled to the coupling plate is assembled to the transmission casing via a sensor body. A spool of a manual valve coupled to the coupling plate is assembled to the transmission casing via a valve body fixed to the sensor body. The coupling plate, the slider and the spool are assembled together, wherein the transmission casing is used as the base for the assembling process. It is not necessary to relatively position the slider and the spool to each other during the assembling process for an oil-pressure control device.