PURPOSE:To reduce the number of machining processes in a lower mount part so as to reduce the cost and secure binding strength between a lower mount housing and a steering shaft while preventing the steering shaft from being thickened. CONSTITUTION:In a lower mount part 11, a steering shaft 31 having a round cross section is clamped by means of lower mount housings 34, 35. Both of the lower mount housings 34, 35 are prevented from rotating by fitting between pins 34b, 35b and through holes 31a. The steering shaft 31 is assembled after molding without requiring any post-processing. Therefore, a joint part between them needs not to be machined, so that the costs can be reduced. As binding strength can be obtained without being affected by the diameter of the steering shaft 31, the steering shaft 31 can be prevented from being thickened unnecessarily.