PURPOSE: To develop an optimum FM modulation wave generation method for an FSK communication system generating a stable transmission signal with a simple system and to provide an inexpensive and stable transmission device through the use of the concerned modulation method.

CONSTITUTION: A storage means 4 recording level signals which are to time- sequentially synthesize and generate FM modulation waves which are to be transmitted, a means generating an address signal which is to be read from the storage means, a means 6 synthesizing the level signals which are sequentially read from the storage means 4 by the address signal and converting them into analog signals are provided. The content of the address signal generation means, which is to be read from the storage means 4 in accordance with a signal content 10, is changed in accordance with a previously set condition. In the transmission device using the FM modulation generation method, said operation is composed by concrete element functions.