A hydraulic actuator is operated using a manual operation device, operations from the manual operation device are stored in the path of an operation signal to a valve controller and these are read out as required and operations similar to those from the manual operation device are outputted to the hydraulic actuator so that repeated operations of the hydraulic actuator are performed automatically. Further, a vibration signal to the hydraulic actuator is added to the operation by the manual operation device and outputted so that operation that is not accurately performed by manual operation is made possible. In the case where repeated operations are performed continuously, a correction operation by the manual operation device is taken into account so that a correction operation which is varied every given amount is made simple. Thus, the present invention can be used where the digging process of a construction machine is made deeper every given amount.