A transmission including: a sun gear forwardly and reversely rotatable by a driving force; a rotary member being forwardly and reversely rotatable, and having a projecting portion; a clutch causing the rotary member to be forwardly rotated and reversely rotated, and not causing the rotary member to be reversely rotated when a predetermined torque is applied; a planetary gear rotatably supported by the rotary member, meshed with and revolved around the sun gear, and rotated by a rotation of the sun gear; a transmission gear meshed with the planetary gear and rotated when the planetary gear is positioned at a predetermined revolution position; a stopper inhibiting the rotary member from being reversely rotated at a rotation position; a switch including a switch lever which the projecting portion contacts when the rotary member is rotated, and detecting a rotational position of the rotary member, the switch permitting the swinging of the switch lever caused by the projecting portion when the rotary member is forwardly rotated and restricting the swinging of the switch lever caused by the projecting portion when the rotary member is reversely rotated; and a saving mechanism saving the switch lever from being forcedly swung when the rotary member is reversely rotated.