A gas analysis device includes a laser light source configured to output a laser beam, an irradiation unit configured to irradiate a measurement region including measurement target gas with the laser beams in plural directions, plural photoreceivers each configured to receive a laser beam having passed through the measurement region and output an electric signal according to intensity of the received laser beam, and an analyzer configured to analyze the physical state of the measurement target gas based on the electric signal output from each photoreceiver. The analyzer sets a function (e.g. two-dimensional polynomial f(X,Y)) representing the physical state (e.g. concentration, temperature) of the target gas at least in the measurement region, and measures the physical state of the target gas by determining a coefficient of each of terms included in the function based on a measured value obtained from the electric signal output from the photoreceiver.