A transmission device for bodybuilding device or bicycle, comprising: an axle, wherein the axle is coupled via a spline to a sprocket assembly, the axle having two ends respectively receiving axle sleeves fit thereto; two cranks, which are respectively the right-hand side crank and the left-hand side crank, the two cranks having operation end axle bores in which a one way bearing is mounted, such that the two cranks are coupled through the one way bearings to outer circumferences of the axle sleeves, the two cranks having surfaces facing towards the axle and provided with a clutch tooth formation; characterized by further comprising: a wire control assembly, which comprises a clamp body comprising an upper clamp member and a lower clamp member mating and combinable with each other, the clamp body being connected through a wire to a wire control switch, an opposite end of the wire being connected through an elastic element to two elbow hook structures; and two clutch control assemblies, which each comprise a slide block, an intermediate ring, and a clutch, the intermediate ring of one of the clutch control assemblies comprising the sprocket assembly that is structured as an intermediate ring-sprocket assembly, wherein the slide block, the intermediate ring or the intermediate ring-sprocket assembly, and the clutch are coupled to each other through three spring screws, the slide block being provided with a spring push peg positioned against and engaging a side recess of the clamp body, the slide block having two sides provided with a square slot pin for hooking engagement with the elbow hook structures to form the transmission device. an axle, wherein the axle is coupled via a spline to a sprocket assembly, the axle having two ends respectively receiving axle sleeves fit thereto; two cranks, which are respectively the right-hand side crank and the left-hand side crank, the two cranks having operation end axle bores in which a one way bearing is mounted, such that the two cranks are coupled through the one way bearings to outer circumferences of the axle sleeves, the two cranks having surfaces facing towards the axle and provided with a clutch tooth formation; characterized by further comprising: a wire control assembly, which comprises a clamp body comprising an upper clamp member and a lower clamp member mating and combinable with each other, the clamp body being connected through a wire to a wire control switch, an opposite end of the wire being connected through an elastic element to two elbow hook structures; and two clutch control assemblies, which each comprise a slide block, an intermediate ring, and a clutch, the intermediate ring of one of the clutch control assemblies comprising the sprocket assembly that is structured as an intermediate ring-sprocket assembly, wherein the slide block, the intermediate ring or the intermediate ring-sprocket assembly, and the clutch are coupled to each other through three spring screws, the slide block being provided with a spring push peg positioned against and engaging a side recess of the clamp body, the slide block having two sides provided with a square slot pin for hooking engagement with the elbow hook structures to form the transmission device. a wire control assembly, which comprises a clamp body comprising an upper clamp member and a lower clamp member mating and combinable with each other, the clamp body being connected through a wire to a wire control switch, an opposite end of the wire being connected through an elastic element to two elbow hook structures; and two clutch control assemblies, which each comprise a slide block, an intermediate ring, and a clutch, the intermediate ring of one of the clutch control assemblies comprising the sprocket assembly that is structured as an intermediate ring-sprocket assembly, wherein the slide block, the intermediate ring or the intermediate ring-sprocket assembly, and the clutch are coupled to each other through three spring screws, the slide block being provided with a spring push peg positioned against and engaging a side recess of the clamp body, the slide block having two sides provided with a square slot pin for hooking engagement with the elbow hook structures to form the transmission device.