PURPOSE: To make it possible to automatically detect the placement of GO (Japanese board game) stones on all the intersected points of the lines and lines on a GO board having the same shape as the shape of a real GO board.

CONSTITUTION: Photodiodes 5 are embedded under the intersected points 4 of the lines and lines of the GO board and light is detected in an area of about 5.0mm×8.0mm of an element 6. At this time, the GO stones 3 are set at such a size at which the GO stones 3 of a size of about 2mm diameter sufficiently shield the light even if the GO stones 3 are placed to deviate from the centers of the intersected points 4 of the lines and the lines. The photodiodes 5 may be embedded into the base material of the GO board and a plate made of translucent plastic contg. figured grain patterns drawn with checkers may be superposed thereon. A microcomputer is embedded together with the photodiodes and is connected to an external display device and keyboard.