PURPOSE: To judge testing possibility within a short time with high accuracy by mounting an apparatus storing the data of test possibility judging condition to collate the same with the logical circuit data at the time of the planning of a logical circuit board and judging the testing possibility of the latter to display the same on a screen.

CONSTITUTION: The logical circuit chart data prepared at the time of the planning of a logical circuit board is stored in a memory apparatus 3. Subsequently, a central processing unit 1 judges whether the logical circuit chart data corresponds to a testing impossible condition at every logical circuit on the basis of the testing impossible condition data held to the apparatus 3 and the logical circuit chart data of a logical circuit board according to the testing possibility judging program of the logical circuit board built in the unit 1 and prepares testing impossible data when said data corresponds not only to hold the said data to the apparatus 3 but also to display the same on a display apparatus 4 and, at the same time, the central processing unit 1 displays the logical circuit chart data on the display apparatus 5 and allows the impossible circuit indicated by impossible circuit data to flash to indicate the impossible circuit.