PURPOSE: To set the times of a rectilinear motion to an arbitrary number with respect to one circular motion by providing a waveform groove or collar on the surface of a cylindrical shaft.

CONSTITUTION: The above shaft 1 can take the place ol a crankshaft used in a compressor or a compression type internal combustion engine. The shaft is used for converting a rectilinear motion to a circular motion or reversely converting same. The motion of a crankshaft is switched at the ratio of rectilinear motion to circular motion 1:1, so that the convertion of energy between the rectilinear motion and the circular motion is not proportional. On the other hand, a shaft having a piston mechanism has to be designed in consideration of the bore ratio, and besides it has the disadvantage that the mechanism is increased in size due to much inavailable energy. Accordingly, the above disadvantage can be overcome by the number of waveforms of the shaft 1.