A sensor information acquisition section acquires angular velocity information (GX, GY, GZ) around three axes acquired by three angular velocity sensors, and acceleration information (AX, AY, AZ) in three axial directions acquired by three acceleration sensors. A posture information calculation section calculates a posture angle and position coordinates in a virtual three-dimensional space based on the angular velocity information (GX, GY, GZ) and the acceleration information (AX, AY, AZ). The posture information calculation section calculates a fixed coordinate system velocity vector based on an inertial coordinate system acceleration vector (A) obtained from the acceleration information (AX, AY, AZ), and calculates position coordinates in a virtual three-dimensional space corresponding to the fixed coordinate system velocity vector.