Balancer device of internal combustion engine

A balancer device of an internal combustion engine, comprising:

• a drive gear that is engaged with an input gear to which a rotation force is transmitted from a crankshaft;
• a balancer drive shaft to which the rotation force is transmitted from the drive gear, the balancer drive shaft having a balancer weight;
• a balancer drive gear that is provided so as to rotate integrally with the balancer drive shaft;
• a balancer driven gear that is engaged with the balancer drive gear;
• and
• a balancer driven shaft that is provided so as to rotate integrally with the balancer driven gear, the balancer driven shaft having a balancer weight, and
• at least one of the drive gear, the balancer drive gear and the balancer driven gear being provided, on both axial direction side surfaces thereof, with ring-shaped grooves whose diameters are different from each other, and
• the ring-shaped grooves being formed up to a depth from the surface of the gear at which both the ring-shaped grooves overlap each other in the axial direction.