In the preset invention, in an initial stationary state of a drumstick section, a CPU stores each axis component of geomagnetism obtained by a magnetic sensor in a RAM, and obtains each axis component of geomagnetism obtained by the magnetic sensor which is changed by a motion provided to the drumstick section at every predetermined timing. Then, the CPU accumulates each axis component of geomagnetism obtained at every predetermined timing, for each predetermined interval, and conforms each axis component of geomagnetism accumulated thereby to each axis component of geomagnetism stored in the RAM.