PURPOSE: To position the cranks of a crankshaft on the arbitrary equally spaced angular positions about the crankshaft axis by mounting a cooperating key means on two ends of each shaft segment and the cooperating holes of the side members.

CONSTITUTION: Two spline holes 11, 12 are formed on a crank side plate 10, the centers of the holes 11, 12 are separated from one another by a distance corresponding to the displacement of a crank pin from a central line of a crankshaft, and the slots 13, 14 are formed. Whereby the holes 11, 12 slightly reduce their diameters when a bolt 18 is put in a hole 17 and clamped by a nut 19. A shaft segment 20 comprises the splines 21 over its total length, comprises a reduced diameter portion on each end, the reduced diameter portions are fitted to the holes 11, 12 of the side plate 10, and a shoulder part is butted to the side plate 10. By cutting the splines 21 so as to form the radial walls, the spline portions are firmly wedged one another by the cooperating clamp of a male spline and a female spline.