To provide a transmission device in which assembly of a shift spindle is improved. In the transmission device, a groove is formed on a shift spindle into an annular shape along the peripheral portion of the shift spindle. A positioning pin is mounted so as to be inserted through a through hole of a rear cover from the outside. The distal end of the positioning pin projecting inwardly of the rear cover is locked with the groove. A rib with which a spindle plate can come into abutment is formed on the inner side of the rear cover. The groove is arranged on the extension of the through hole in a state in which the spindle plate comes into abutment with the rib.