A tension detection mechanism includes a linear member which extends in a longitudinal direction, and which is configured to transmits power, a restraining member including a restraining portion through which the linear member extends and which is configured to restrain movement of the linear member in the longitudinal direction partially, and a detection member which is provided to the restraining member and which is configured to detect tension of the linear member. A length of a portion of the linear member restrained by the restraining portion is larger than a distance between two ends of the restraining member in the longitudinal direction of the linear member.