A building management system for one or more buildings, having a processor and a display for showing a model of a building being managed. The transmitter includes a generator of a chip clock, a generator of a spreading code sequence of a fixed chip rate by using the chip clock, and a frequency converter of a carrier wave frequency, being synchronous with the chip clock, by a transmission signal spread-modulated by the spreading code sequence. The light emission device may include plural semiconductor light emitting elements having a different wavelength ranges such as diodes stacked in a compact and predetermined order such that wavelengths of light from each diode are emitted from the light emitting elements.