Abstract: The pyrometer includes at least one optical fibre (10) transparent to infra-red made of fluorite glass, a reference emitter (20) of infra-red flux, an infra-red detector (30) for receiving the infra-red flux emerging from the optical fibre (10) or the infra-red flux originating from the reference emitter (20), a mechanical modulator (40) for infra-red flux positioned, in the direction of flux propagation, upstream of the infra-red detector (30) for periodically and successively interrupting the infra-red fluxes emerging from the optical fibre (10) and originating from the reference emitter (20), an electronic means of demodulation (50) for receiving the output signal from the detector (30) and a servo-control signal emitted by the mechanical modulator (40) in order to ensure a synchronized measurement, and a measuring apparatus (60) connected to the electronic demodulation means (50) for indicating the temperature to be measured of the target irradiating the optical fiber.