A plurality of amplifiers and PCs each having installed therein remote controlling software for controlling the amplifiers are connected to a network. Data stored in a memory of each of the amplifiers include a device ID, operation data and an area ID. Memory of each of the PCs stores therein a project file each including area IDs, device information and device IDs. On the basis of the area IDs and device IDs stored in the amplifiers and the area IDs and device IDs stored in the project file, a CPU of the PC performs association between the amplifiers and virtual devices indicated by the device information and overwrites the operation data of a particular amplifier, having been associated with any one of the virtual devices, onto the project file, to thereby display, on a display, the operation data of the associated amplifier as operation data of the corresponding virtual device.