PURPOSE: To perform the execution processing of a logical language at a high speed by changing the processing order of respective terms so that the execution processing of the logical language is terminated with a smaller number of processing steps.

CONSTITUTION: An execution processing device of the logical language is provided with an input/output device 11, an arithmetic unit 12, a work storage device 13 attached to the arithmetic unit 12, a program storage device 14 of the inputted logical language, an execution processing program storage device 15 of the logical language, and a predicate relation extracting program storage device 16. The largest number of rules are used to preferentially select terms leading a fact when a variable exists in a question in the stage of execution processing, and the smallest number of rules when any variable does not exist in the question, thereby dynamically and finely controlling term selection. Thus, the quick execution processing where the number of times of retrogressive processing is smaller is executed.