To provide a muscular drive mechanism ideal for a muscular driven vehicle or equipment imitating the vehicle such as a bicycle, a tricycle, a quadrecycle, a wheelchair, a boat, a muscular airplane and training equipment, compact, comfortable and capable of effectively converting manual force into power.

A pair of rotation body and support body formed of vertically provided sprockets, and a chain wound around these rotation body and support body are disposed on either side. The left and right rotation bodies 1, 100 are fixed to a driving shaft 15, and a chain ring 6 to which load is applied, is fitted between the rotation body 1 and rotation body 100 on the driving shaft 15. A pedal shaft is kept always vertical to the moving face of the chain by a restraining means comprising a free crank bent toward a fitting part on a frame, and an arm provided inside the free crank and connected to the free crank. The use of the free crank bent toward the fitting part on the frame permits the miniaturization of a device and the increase of rigidity and realizes the high-output manual drive mechanism comfortable with little aerodynamic resistance.