A throttle valve 10 continuously increases/decreases the flow rate of air flowing through a communication hole 17 through which a first port 11 and a second port 12 are communicated with each other, by using a throttle valve element 22. A valve seat member 15 having the communication hole 17 is attached to a housing 13. An electric motor 25 is attached to a motor housing hole 24 formed in the housing 13. The throttle valve element 22 is driven in an axial direction by a motor shaft 28 of the electric motor 25. A gap between the motor housing hole 24 and the electric motor 25 is sealed by a fixed sealing member 41 having a large diameter, and the motor shaft 28 is sealed by a rotary sealing member 42 having a small diameter, whereby the throttle valve element can be driven by the electric motor having a small output.