Interference monitoring device

An interference monitoring device that makes a check on interference between a tool and a workpiece in a machine for performing predetermined machining on the workpiece while moving the tool and the workpiece relative to each other based on a program, the interference monitoring device comprising:

• a processor configured to:
• calculate an advanced position of the tool or the workpiece ahead by a predetermined period of time based on the program;
• draw an estimated shape of a machined part of the workpiece based on the advanced position, and make the interference check based on the estimated shape of the machined part of the workpiece;
• and
• calculate an error between the estimated shape of the machined part of the workpiece and a stored shape of the machined part of the workpiece as an uncut region in the estimated shape of the machined part of the workpiece, wherein
• the interference check is not made in the uncut region,
• the estimated shape of the machined part of the workpiece is drawn while the machining is being performed, and
• the stored shape of the machined part of the workpiece is stored prior to the machining being performed.