To realize smooth movement, miniaturize a crank device, and reduce the man-hour of assembly by providing a crank pin formed at a specific distance from a crank shaft, a ball pin in an outer peripheral part of a planetary gear, a connection bar which is rotatably supported on the ball pin and has a regulation rail, and a regulation member provided in a housing.

A crank shaft 7a of a crank mechanism 7 is rotatably supported by a bearing 8 of a housing 5 and is rotated by a motor. Consequently, a crank arm 7b and a crank pin 7c also move together on circumference having a radius of L1 centered on the crank shaft 7a. A planetary gear 6b rolls along an inner periphery of a sun gear 6a, and a ball pin 10 in an outer peripheral part of the planetary gear 6b reciprocates in a scope double L1 centered on the crank shaft 7a on line A-A. A connection bar 1 supported by the ball pin 10 reciprocates, and a piston 3 reciprocates vertically in a cylinder 4 by regulation members 2a to 2e. Consequently, the destruction of a connection part of the connection bar and the planetary gear due to the inclination of the ball pin is prevented, and a crank device can be made compact.