A throttle device for engine has a throttle valve, a shaft, and a valve gear. The valve gear is driven to rotate by a motor. The shaft and the valve gear are unitarily molded of a continuous resinous material. In the coupled area between the shaft and the valve, a recess section is provided. The recess section is formed, from the outer end face of the gear, coaxially with the shaft. The recess section serves as a thin-walled section, and prevents deformation of the gear likely to be caused by heat shrinkage. Furthermore, the recess section includes a through hole, which is effective for moving the ball bearing along the axial direction. A press-fitting tool is inserted into the through hole to install the ball bearing by pressing.