A shift drum angle detecting device for a transmission includes shift forks, a shift drum, a first sensor shaft, a first angle sensor, a speed increasing mechanism, and a second angle sensor. The first angle sensor is to detect a rotational angle of the first sensor shaft to output a first output value based on the rotational angle. The speed increasing mechanism includes a speed increasing drive member, a speed increasing driven member, and a second sensor shaft. The second angle sensor is provided to the second sensor shaft to detect a rotational angle of the second sensor shaft and to output a second output value based on the rotational angle. A rotational angle of the shift drum is to be detected based on the first output value output from the first angle sensor and the second output value output from the second angle sensor.