An electric toothbrush includes a gyro sensor inside a main body. The gyro sensor detects an angular velocity of the main body and the main body includes a head portion, a neck portion, and a grip portion in a longitudinal axis direction. An angle formed by a longitudinal axis of the main body in a state that brush bristles of the head portion contact with a brushing site in a dentition with respect to the longitudinal axis of the main body in a state that the brush bristles of the head portion contact with a reference position in the dentition is obtained, based on an output from the gyro sensor. A corresponding point corresponding to the brushing site on an approximate curve that curves corresponding to the dentition is obtained based on the angle, and coordinates of the corresponding point are used as a translational position of the brushing site.
