Abstract: A controller is obtained by adding the function of a virtual operator to a numerical control device. Data on the construction and capacity of a machine, as a control object, are stored as system data in advance. Work instructions are inputted by the operator or through a host system. The virtual operator, comparing the contents of the work instructions with the system data, determines whether automatic processing is possible or manual processing is required. If the automatic processing is possible, the automatic processing is carried out. If the manual processing is necessary, explanation diagrams, messages, etc. are displayed. Every time a request button for further explanation is depressed, a more detailed work explanation is displayed. Thus, the operation is simplified, and the work explanation can be obtained according to the skill of the operator.