PURPOSE: To design a logic circuit that a designer can easily understand in a short time.

CONSTITUTION: This designing device is equipped with a syntax analytic part 12 which analyzes the syntax of a behavior description 11 and outputs connection data 13 on arithmetic, storage element information 14a, and information 14b used for the arithmetic, an outline designing part 16 which designs an outline according to the storage element information 14a, the information 14 used for the arithmetic, and restriction conditions 15 to generate bus constitution 17a and a function block 17b, and a detailed designing part 18 which performs detailed designing by using the connection data 13 on the arithmetic, the bus constitution 17a, and the function block 17b to generate the logic circuit 19.