An internal combustion engine (18) has an intake pipe (34) which extends from an internal combustion engine main body (19) and an intake passageway (33) formed in the interior thereof communicates with an intake passageway (27) formed in the internal combustion engine main body (19), a fuel supply means (36) for supplying fuel to the internal combustion engine main body (19), an intake negative pressure sensor (43) for detecting an intake negative pressure (P) in the intake passageway (33) within the intake pipe (34), and a control unit (44) for controlling the supply of fuel to the internal combustion engine main body (19) by the fuel supply means (36) based on a detection signal of the intake negative pressure sensor (43). The intake negative pressure sensor (43) is adapted to detect an intake negative pressure at a downstream end (42) of the intake passageway (33) within the intake pipe (34). According the intake negative pressure sensor (43), the value of the intake negative pressure (P) in the intake passageway (27) in the internal combustion engine main body (19) is detected accurately.