PURPOSE: To provide a smoke and flame composite sensor and smoke and flame composite sensing system which judge a fire with high precision corresponding to the actual installation environment and prevents misalarming in a non-fire state by totally judging detected smoke and flame.

CONSTITUTION: The sensor and sensing system are equipped with a smoke sensing part 1 which detects the presence of smoke and outputs a smoke detection signal, a smoke signal processing part 2 which converts this smoke detection signal into a multistage signal, a flame sensing part 3 which detects the presence of flame and outputs a flame detection signal, a flame signal processing part 4 which converts the flame detection signal into a multistage signal, a flame judgement part 5 which makes a flame/non-flame judgement according to the multistage signals outputted from the smoke signal processing part 2 and flame signal processing part 4, and a signal output part 6 which outputs the judgement result of this flame judgement part 5 to a receiver or repeater through a signal line L.