To provide a body movement detector that communicates with another body movement detector to transmit and receive acceleration data.

Information indicating activity intensity calculated from the number of steps measured as information on the number of steps is transmitted from a pedometer 100A to a pedometer 100B (S7). In the pedometer 100B, the affinity of walking is determined based on a difference between the activity intensity of the pedometer 100A and the activity intensity of the pedometer 100B (S9), and the result of determination is displayed on the both pedometers (S13A, S13B).