To provide an internal combustion engine of a vertical shaft type, in which leakage of an oil from a crankcase and an oil pan is effectively prevented, which has high mounting rigidity relative to a working machine and, also, which is capable of being easily serviced, the combustion engine includes a vertically extending crankshaft (9) having a pair of upper and lower crank webs (14A and 14B), a crankcase (1) accommodating the crankshaft (9) and including an oil pan (2), and a crankcase cover (3) mounted on an upper surface (1a) of the crankcase (1) to cover the crankcase (1). The upper surface (1a) of the crankcase (1) is positioned above the upper crank web (14A).