PURPOSE: To improve the warming of machine in the exhaust system without deteriorating the idle operating performance during cool time of engine, by closing the suction control valve under idle operation while fully opening during operation other than idle operation if the level of the warming of machine for an internal-combustion engine is below predetermined level.

CONSTITUTION: When the cooling water temperature of an internal-combustion engine is below predetermined level, the port (a) of a temperature sensing exchange valve 27 is coupled to the port (c) to lead the pressure appearing in the suction tube negative pressure take-out port 36 into the diaphragm chamber 23. Under idle operation, a valve element 17 will fully close while fully open under other operation. When the cooling water temperature is higher than predetermined level, the port (a) of a temperature sensing valve 27 is coupled to a port (b). When it is operated with low or intermediate air flow, the valve element will be at the fully closed position. Upon increase of the load or rotation of the internal-combustion engine, the suction air flow will increase to increase the negative pressure from a Venturi negative pressure take-out port 38 thus to open an atmospheric open valve 50 while closing the valve element 17.