PROBLEM TO BE SOLVED: To provide an externally attached type normal/reverse rotation switch unit which can switch rotations of an output shaft of an engine between a normal rotation direction and a reverse rotation direction.SOLUTION: A normal/reverse rotation switch unit 1 in this invention includes: a first drive shaft 71 connected to an output shaft 12 of an engine 11 a second drive shaft 73 provided in a fixed state to be parallel to the first drive shaft 71 a reverse rotation mechanism 79 having a drive gear 75 mounted on the first drive shaft 71 in a fixed state and a driven gear 77 which is mounted on the second drive shaft 73 in an idling state and meshes with the drive gear 75 a first power transmission mechanism 81 which transmits rotations of the drive gear 75 to an input shaft 14 of a power conversion mechanism 13 a second power transmission mechanism 83 which transmits rotations of the driven gear 77 to the input shaft 14 of the power conversion mechanism 13 and a power transmission switching mechanism 85 which selectively switches the first power transmission mechanism 81 and the second power transmission mechanism 83 between a power transmitted state and a power non-transmitted state.
