An offline programming device includes an input unit that receives input of a plurality of teaching points, a creation unit that determines intermediate point located between adjacent teaching points and creates an operation program for the robot, a simulation unit that simulates a movement trajectory of the robot when the operation program is executed, and a display unit that displays a GUI screen representing the movement trajectory. The GUI screen includes a first display area showing a time series sequence of the plurality of teaching points and a second display area. When an error is detected in the movement trajectory, a section between the teaching points including the point in time when the error occurs is displayed in the first display area according to a first error display method.

A machining state diagnosis apparatus (10) includes a machining state information estimation device (1), a learning information storage (11) storing information on relationship between estimated machining state information and actual machining state information, and a machining state diagnosis unit (12) diagnosing a machining state in actual machining using control information, based on machining state information obtained during the actual machining, machining state information estimated based on corresponding control information by the machining state information estimation device (1), and the relationship information stored in the learning information storage 11. The machining state information estimation device (1) includes an information storage (2) storing the control information and information on a workpiece and a tool, a machining state information estimator (3) estimating machining state information in relatively moving the workpiece and the tool, based on the information on the workpiece and the tool and the control information, and an image data generator (4) generating image data based on the estimated machining state information.