A housing 1 contains a plurality of signal processing units for performing signal processing corresponding to a plurality of operation modes. At a front surface 1a of the housing, an operation panel 3, a display, and a plurality of signal terminals 5a are provided, the signal terminals being located close to the display and shared by the signal processing units. A signal name memory stores signal names 11 allocated to the respective signal terminals for each of the signal processing units. A changeover switch is switched such that the signal processing units are connected to the signal processing unit corresponding to the designated operation mode in response to the operation-input operation mode designation, and the signal name corresponding to the designated operation mode is read out from the signal name memory, and is then displayed in the vicinity of the corresponding signal terminal on a display screen 4a of the display.