To promote warm-up, prevent a throttle body from freezing, and suppress slapping sound of a piston.

A cooling system 100 includes: a first circulation path in which a coolant discharged from a water pump 1 returns to the water pump 1 by way of an engine 2, an electric valve 3, a heater core 41, and an EGR cooler 42 (waste heat recovery device 43), and a thermostat 11 in sequence; and a second circulation path in which the coolant discharged from the water pump 1 returns to the water pump 1 by way of the engine 2, the throttle body 51, an EGR valve 52, and the thermostat 11 in sequence. In an engine block 2A (refer to Fig.2), the second circulation path is formed so as to communicate with an upper part of the engine block.