PURPOSE: To prevent abnormal rise of catalyst temperature at the time of deceleration coasting and to reduce a harmful exhaust component by providing a control part setting second control engine speed for idle up control higher than first control engine speed for fuel cut control.

CONSTITUTION: An actuator 12 is communicated to a solenoid valve 16 by a first communication passage 14. The solenoid valve 16 is communicated to the downstream side of an inlet passage 4 by a second communication passage 18 and to a control part 20. Additionally, in the control part 20, first control engine speed for fuel cut control and second control engine speed for idle up control of a travel range, for instance, D range higher than this first control engine speed are set. Consequently, when engine speed of an internal combustion engine becomes the first control engine speed, the control part carries out the fuel cut control, and when it becomes the second control engine speed, the control part 20 carries out the idle up control. Accordingly, at the time of a long time and high speed inertial state, it is possible to prevent rise of catalyst temperature.