PURPOSE: To make the operation speed higher and improve the control precision by setting an operation formula for calculation of a target value in the high level language of a computer by the user side and executing the operation in the level of a machine language.

CONSTITUTION: A coding means codes an optionally set operation formula and supplies it to an interpreting means. The interpreting means converts the supplied coded operation formula to an operation program in the machine language and supplies it to a program executing means. If a variable exists in this set operation formula, the measured value is inputted momently to the program executing means to execute the operation program and the target value for driving a servo mechanism is calculated and outputted.