While an information display device is initially placed at a standstill, a CPU stores acceleration responsive to gravitational force acquired by an acceleration sensor into a RAM. The CPU acquires acceleration in compliance with fixed timing acquired by the acceleration sensor and resulting from motion on the information display device. The CPU accumulates the acceleration acquired in compliance with the fixed timing within each prescribed period. Then, the CPU makes the accumulated acceleration agree with acceleration responsive to gravitational force stored in the RAM, thereby correcting a posture parameter. Based on the corrected posture parameter, the CPU determines whether a temporal image is to be displayed on a display unit.