In order to improve the efficiency of test and debug procedure based on delarative program understanding of a program described by a logical language, the operation which has been executed for each procedure is grasped. On the basis of information relating to the grasped operation, the operation range of each procedure is expressed clearly by making thick only sides which have actually operated among four sides of a box-shaped figure surrounding each head term and end body term of each clause included in each procedure.
A sequence of calling clauses and all clauses in a procedure that includes the selected clauses are displayed simultaneously, and the present point of execution is displayed being overlapped on the above displays. In particular, the program source list of a procedure being processed is displayed, and the latest execution statuses of the executed terms are graphically displayed around the terms on the displayed program source list.
