PURPOSE: To upgrade the starting property of the movement of a timed annular balance while improving th workability thereof by initially striking a dowel pin with a fine rotary torque of an escape wheel gear to hit and drive a balance wheel through a balance wheel control pin.

CONSTITUTION: A balance stem 8 has a small-diameter step 9, a large diameter section 10 with a carrier 11 and a fine diameter section 12. A balance wheel 13 is provided with a loose-fit hole 14 and a pin hole 15. A pair of dowel pins 17 are erected on a dowel pin anchor plate 16 while a balance wheel control pin 18 is formed on the back thereof. A slight clearance is retained between the balance wheel 13 and the carrier 11 on the large-diameter section 10 of the stem 8 and after the insertion of the small-diameter step 9 into the loose-fit hole 14, a center hole 19 of the anchor plate 16 is fitted into the fine-diameter section 12. The balance wheel 13 is so arranged to be inserted loosely into the pin hole 15 in the direction of rotation by a difference in the diameter of the balance wheel 18 on the anchor plate 16.