In the preset invention, in an initial stationary state of a drumstick section, a CPU stores acceleration that occurs due to gravity and is obtained by an acceleration sensor in a RAM, obtains, at every predetermined timing, acceleration that occurs due to a motion provided to the drumstick section and is obtained by the acceleration sensor at a predetermined timing, accumulates the accelerations each obtained at the predetermined timing for each predetermined interval, and conforms the accelerations obtained by accumulation to the acceleration stored in the RAM.