To provide a detector for an infrared gas analyzer having high sensitivity and hardly affected by ambient temperature.

In this detector 1 for an infrared gas analyzer filled with gases G expressing same absorption characteristics of a measurement target gas and provided with two gas chambers 114, 15 arranged in series to each other relative to a measurement cell 2, the gas chambers 14, 15 are communicated with each other via a gas passage 16, the gas passage 16 is provided with a pyroelectric flow detecting element 19, the detection part 20 of the pyroelectric flow detecting element 19 is heated by a heater 27, and a voltage impressed on the heater 27 is controlled according to the temperature of the detector 1.