PURPOSE: To improve operability by arranging the two pairs of detectors to detect movement in the same plane at least in one case while separating them.

CONSTITUTION: On the side faces of an A ball 2 and a B ball 3 to be rotated with the movement of a horizontal plane, two encoders 21 and 22 and an encoder 31 are arranged to detect the rotating amounts of the respective balls in two directions orthogonal each other. The encoders 21 and 31 respectively detect the rotating amounts in parallel directions. In this case, when a main body case 1 is moved while being rotated, moving amounts ΔX and ΔY per unit time and a rotating angle ΔQ of the main body case 1 are calculated by ΔX=ΔXA or ΔX=(ΔXA+ΔXB)/2, ΔY=ΔYA, ΔQ=(ΔXA-ΔXB)/D and θ=ΣΔθ. Namely, since the two pairs of move detectors are built in the main body case 1, when the main body case 1 is moved while being rotated, graphics can be rotated synchronously with this rotation.