Mechanical timepiece

A mechanical timepiece, comprising:

• a power source;
• a speed governing mechanism including:
• a balance wheel to be driven by motive power supplied from the power source;
• and
• a hairspring to be elastically deformed so as to cause the balance wheel to perform a forward/reverse rotational motion;
• a permanent magnet which includes a first polarity portion and a second polarity portion having a polarity different from a polarity of the first polarity portion, and which is configured to perform a forward/reverse rotational motion along with the forward/reverse rotational motion of the balance wheel;
• a coil;
• a soft magnetic core including:
• a first end portion provided so as to cause a magnetic resistance with respect to the permanent magnet;
• and
• a second end portion provided on a side opposite to the first end portion through intermediation of the permanent magnet so as to cause a magnetic resistance with respect to the permanent magnet;
• and
• a control circuit for performing rate adjustment based on a detection voltage and a normal frequency of a reference signal source, the detection voltage being caused in the coil by a motion of the permanent magnet accompanying a forward direction motion and a reverse direction motion of the balance wheel,
• wherein the permanent magnet is arranged so that:
• at a first angle position under a state in which the hairspring is brought to a neutral position of elastic deformation thereof, the first polarity portion is opposed to the first end portion with a first interval, and the second polarity portion is opposed to the second end portion with a second interval;
• at a second angle position rotated by 180° from the first angle position, the first polarity portion is opposed to the second end portion with a third interval, and the second polarity portion is opposed to the first end portion with a fourth interval;
• and
• the second interval is smaller than the first interval, and a difference between the fourth interval and the third interval is smaller than a difference between the first interval and the second interval.