To provide a structure of a crank for a bicycle capable of enhancing productivity without sacrificing high strength and a lightweight property.

In the crank for the bicycle, first and second members of C-shaped sections are fitted so that inner faces of both C-shaped arms of the second member are abutted on outer faces of both C-shaped arms of the first member. The direction of the moment applied when stepping in a right pedal is defined positive, and the direction of the moment applied when stepping in a left pedal is negative. Signs of four bending-torsion coupling terms 113, 123, 132 and 131 of the elastic compliance of the first member are opposite to those of the moment applied during the step-in operation, and signs of four bending-torsion coupling terms 213, 223, 232 and 231 of the elastic compliance of the second member are the same as those of the moment during the step-in operation.