A speed change device for a motorcycle including: a shift operating member, a shift spindle (51, 101, 121), a link mechanism connecting the shift operating member to the shift spindle (51, 101, 121) so as to rotate the shift spindle (51, 101, 121) according to an operation of the shift operating member, a shift drum, a shift drum driving mechanism for rotating the shift drum by transmitting rotation of the shift spindle (51, 101, 121) to the shift drum, a shift fork engaging with the shift drum to select one speed change stage by transmitting rotation of the shift drum to a shifter gear of a transmission, and a shift stroke sensor attached to a lost motion mechanism, the lost motion mechanism being associated with a shift rod member of the link mechanism and transmitting an operating force by an elastic member, the shift stroke sensor detecting an amount of expansion/contraction stroke of the shift rod member, the speed change device being characterized by comprising: a shift spindle sensor (55, 105, 125) for detecting rotation of the shift spindle (51, 101, 121); and an output control device for controlling output of an internal combustion engine on the basis of a detection signal of the shift stroke sensor and a detection signal of the shift spindle sensor (55, 105, 125); the shift spindle (51, 101, 121) having a circular cylindrical outer circumferential surface and a detection-target recessed portion (51X, 101X, 121X) formed by recessing a part of the cylindrical outer circumferential surface, the shift spindle sensor (55, 105, 125) being configured to cooperate with the detection-target recessed portion (51X, 101X, 121X) to detect the rotation of the shift spindle (51, 101, 121). a shift operating member, a shift spindle (51, 101, 121), a link mechanism connecting the shift operating member to the shift spindle (51, 101, 121) so as to rotate the shift spindle (51, 101, 121) according to an operation of the shift operating member, a shift drum, a shift drum driving mechanism for rotating the shift drum by transmitting rotation of the shift spindle (51, 101, 121) to the shift drum, a shift fork engaging with the shift drum to select one speed change stage by transmitting rotation of the shift drum to a shifter gear of a transmission, and a shift stroke sensor attached to a lost motion mechanism, the lost motion mechanism being associated with a shift rod member of the link mechanism and transmitting an operating force by an elastic member, the shift stroke sensor detecting an amount of expansion/contraction stroke of the shift rod member, the speed change device being characterized by comprising: a shift spindle sensor (55, 105, 125) for detecting rotation of the shift spindle (51, 101, 121); and an output control device for controlling output of an internal combustion engine on the basis of a detection signal of the shift stroke sensor and a detection signal of the shift spindle sensor (55, 105, 125); the shift spindle (51, 101, 121) having a circular cylindrical outer circumferential surface and a detection-target recessed portion (51X, 101X, 121X) formed by recessing a part of the cylindrical outer circumferential surface, the shift spindle sensor (55, 105, 125) being configured to cooperate with the detection-target recessed portion (51X, 101X, 121X) to detect the rotation of the shift spindle (51, 101, 121). a shift spindle sensor (55, 105, 125) for detecting rotation of the shift spindle (51, 101, 121); and an output control device for controlling output of an internal combustion engine on the basis of a detection signal of the shift stroke sensor and a detection signal of the shift spindle sensor (55, 105, 125); the shift spindle (51, 101, 121) having a circular cylindrical outer circumferential surface and a detection-target recessed portion (51X, 101X, 121X) formed by recessing a part of the cylindrical outer circumferential surface, the shift spindle sensor (55, 105, 125) being configured to cooperate with the detection-target recessed portion (51X, 101X, 121X) to detect the rotation of the shift spindle (51, 101, 121).