PURPOSE: To obtain such a spherical gear that enables increase of engaging contact area and large torque transmission, can reduce vibration and noise, can realize smooth engagement even if there is an error in parallelism of the center of each gear, and can be used even when the center of rotation crosses.

CONSTITUTION: A device is constituted of a positive spherical gear 1 wherein a tooth shape element of a spur gear is formed in a concentric spherical projected surface whose center is at a point at the center of rotation and a negative spherical gear 2 wherein a tooth shape element of a spur gear is formed in a concentric spherical recessed surface whose center is at a point at the center of rotation of the positive spherical gear 1.