To provide a clock instrument etc., capable of timing the time of an athlete while preventing the erroneous detection of electro-magnetic field.

A wireless tag 50 as shown in (a), while moving 1m width of magnetic field, a plurality of data receiving (acquisition of data ID) can be performed. Therefore, the wireless tag 50 as shown in (b), when received a plurality-th gate ID, the data is determined, after that stands by for L interval which is longer than 30 mS. The wireless tag 50 as shown in (c) acquires the time T3 of second falling timing after the data determination, and the time T4 of next rising timing. Because the time (T4-T3) is longer than 30 mS, the wireless tag 50 obtains the mean time of the time T3 and the time T4 by the (T3+T4)/2, and specifies the time as the athlete time.