PURPOSE: To reduce the number of component parts and an assembling accuracy to lower a cost by supporting a pair of bobbins movably in the axial direction thereof and in the direction orthogonal thereto within a predetermined range.

CONSTITUTION: On the both sides of an outer frame 2, two pairs of circular hole parts 6a, 6b and 6c, 6d are respectively formed with a hole diameter larger than the axial diameter of bobbins 4, 5. The bobbin 4 is formed to be axially longer than a dimension between the both sides of the outer frame 2 and provided with a drive gear 7 on the side of a projection 4a. In the state that an upper half 2a is detached, the both ends of the bobbin 4 are projected from the hole parts 6a, 6b of a lower half 2b, the gear 7 is disposed outside the outer frame 2, and the bobbin is supported by the hole parts 6a, 6b at the two points in the vicinity of the ends thereof. By attaching the upper half 2a, the bobbin 4 is allowed to move freely in the axial direction thereof and in the direction orthogonal thereto within the hole parts 6a, 6b.