Internal combustion engine

An internal combustion engine, comprising:

• a crankcase;
• a case cover for covering a side of the crankcase;
• a crankshaft and a balancer shaft;
• a balancer including a balancer driven gear and a balance weight provided on the balancer driven gear, the balancer being acted upon and driven by a driving force of the crankshaft to rotate;
• and
• an oil pump accommodated in the crankcase and having an oil pump driving shaft disposed in parallel to the crankshaft and the balancer shaft, the oil pump including a pump driven gear;
• wherein the balancer has a pump driving gear having a diameter smaller than the diameter of the balancer driven gear and rotates together with the balancer driven gear, the pump driving gear meshing with the pump driven gear;
• and
• the oil pump driving shaft is disposed within a range of rotation of the balance weight as viewed in an axial direction thereof;
• wherein the crankcase is configured from divisional upper and lower side halves, and the balancer and the oil pump are disposed on a lower side half of the crankcase while the oil pump driving shaft is disposed below the balancer shaft.