To highly precisely drive for opening and closing two throttle valve, respectively arranged in two systems of intake passages, by interlocking with each other through simple structure.

A valve stem 14 is rotatably supported in a manner to traverse first and second intake passages 11 and 12 formed in a throttle body 10, and a first throttle valve 23 consisting of a butterfly valve to open and close the first intake passage 11 and a second throttle valve 24 consisting of a rotary valve to open and close a second intake passage 12 are arranged on the valve shaft 14. Compared with a device to interlock the first and second throttle valves 23, 24 trough a link mechanism, reduction of precision of the opening area of the intake passage due to an influence of rattle is suppressed to a minimum as the number of parts is decreased and a cost is reduced. Besides, a load to open and close the first and second throttle valves 23, 24 is decreased.