To provide an infrared detecting device capable of specifying the kind of a device radiating infrared rays radiated toward its own vehicle.

The infrared detecting device is provided with an infrared detector 1 for detecting infrared rays, an amplifier 2 for amplifying a received signal detected by the infrared detector, a light kind judging part 3 for judging the kind of the received infrared rays based on the amplified signal amplified by the amplifier, and an alarming device 4 for generating alarming output based on the judging result of the light kind judging part. The light kind judging part monitors the presence/absence of a pulse every reference monitoring period (generating interval of communication light) after receiving the infrared ray first, e.g. and judges that the infrared rays are emitted from an automatic velocity regulating device in the case of detecting no pulse, from an automatic number reader when detecting a pulse after the absence of the pulse in a fixed period and from communication equipment in the case of detecting the pulse in all the periods.