Upon detection of an error such as a malfunction occurring at a drive mechanism, a sensor transmits an error signal to a control section. The control section selects character information about details of the error corresponding to the error signal and an image representing the drive mechanism where the error occurs and a position of the sensor in the drive mechanism, and reads out the character information and the image from a storage part. Then, the control section allows a liquid crystal display device to display error information in which a first image of character information is combined with a second image of an error occurrence site in the drive mechanism. After correction of the error, an operator touches a GUI on a screen to thereby check an operation of the drive mechanism.