To provide a communication signal generating circuit, a communication signal output circuit and a communication circuit that can simultaneously generate, output and transmit a communication digital signal and a communication analog signal with a simple circuit configuration or by means of a configuration of communication signal data.

A central processing means 10 of a communication signal generating circuit 11 calculates a process variable and generates a communication signal. In this case, the means 10 generates the communication signal in a way that a duty ratio for an optional prescribed period corresponds to a value of an analog signal for the communication signal when it is outputted as the analog signal by controlling the duty ratio for the optional prescribed period. The communication signal is outputted as a digital signal itself and also outputted via a D/A converter 12 of a simple configuration such as an RC circuit.