A telephone incoming signal discriminator includes a first relay, an FSK detector, a DTMF detector, a pin detector, a tone amplifier and oscillation control, an FSK/DTMF decoder IC, a memory, a buzzer, a comparison/setting control IC, an auto answer machine, and a second relay. When a telephone signal is received, it is detected by the FSK detector and the DTMF detector, decoded by the FSK/DTMF detector IC, and then compared with a set code by the comparison/setting control IC, so that the comparison/setting control IC drives the telephone to ring when matched, or switches on the second relay for enabling the incoming telephone signal to be shifted to the auto answer machine when not matched.