a first microprocessor controls an actuator according to a control program stored in a program storage memory , using a learnt value stored in a learning value storage memory . the learnt value is updated in response to an action of the actuator . a second microprocessor is connected to the first microprocessor to replace the control program with another control program which also has a function to initialize the learnt value . however , when the learnt value has been updated , the first microprocessor prohibits the second microprocessor from replacing the control program , thereby preventing the impairment of control response due to initialization of the learnt value .