To provide a power converting apparatus capable of performing continuous load operation by reducing thrust loads applied to the side walls of cylinders in a mechanism alternately converting the reciprocating motions of pistons and the rocking motion of an oscillating shaft.

In the mechanism alternately converting the reciprocating motions of the pistons and the rocking motion of the rocking shaft, at least two cylinders C1 and C2 are radially installed about the rocking shaft R2, and the pistons P1 and P2 performing reciprocating motion in the cylinders and a rocking shaft arm RA1 fixed to the rocking shaft are connected to each other through connecting rods CR1 and CR2. Thus, since the ratio of the length of the connecting rods to the rocking shaft arms can be arbitrarily set up, the continuous operation can be performed by reducing the thrust loads.