A mechanical time piece of the invention is characterized in including a stud holder (1310) provided rotatably to a central axis line of a balance with hairspring (1340), a hairspring holder (1312) attached to the stud holder (1310) to be movable in a direction orthogonal to the central axis line of the balance with hairspring (1340) and a hairspring (1340c) the portion toward the center of which is fixed to the balance with hairspring (1340) and the portion toward the periphery of which is fixed to the hairspring holder (1312). According to the mechanical time piece of the invention, an eccentric pin (1316) is rotatably attached to the stud holder (1310), the eccentric pin (1316) includes an eccentric hole (1316b) and the hairspring holder (1312) is integrated to the eccentric hole (1316b). Further, it is preferable to constitute the mechanical time piece of the invention such that the mechanical time piece includes a hairspring holder setscrew (1314) for fixing the hairspring holder (1312) to the stud holder (1310), the eccentric pin (1316) includes a lateral hole (1316e) formed to be directed to a central axis line thereof and the hairspring holder (1312) is fixed because the front end of a hairspring holder setscrew (1314) penetrates the lateral hole (1316e) of the eccentric pin (1316) and presses the hairspring holder (1312).