A laser gas analyzer, comprising a light source portion which emits frequency-modulated laser light, a first optical system which collimates light emitted from the light source portion, a second optical system which condenses transmitted light which has propagated from the first optical system via a space in which gas for measurement exists, a light-receiving portion which receives light condensed by the second optical system, and a signal processing circuit which processes an output signal of the light-receiving portion, wherein the light source portion comprises: a laser driving signal generation portion configured to combine a wavelength scanning driving signal that varies the emission wavelength of a laser element so as to scan the absorption wavelength of the gas for measurement and a high-frequency modulation signal to modulate the emission wavelength, and to output the result as a laser driving signal; a current control portion which converts the laser driving signal output from the laser driving signal generation portion into a current; and the laser element to which the current output from the current control portion is supplied; wherein the signal processing circuit is configured to detect, from the output signal of the light-receiving portion, a signal of a component at twice the frequency of the modulation signal modulating the emission wavelength, and measure the concentration of the gas for measurement; and wherein the signal processing circuit comprises: a synchronous detection circuit which detects the amplitude of the signal of the frequency-doubled component from the output signal of the light-receiving portion; and a computation portion configured to determine the concentration of the gas for measurement from the difference between a maximum value and a minimum value of a gas absorption waveform existing in the output signal (Sb) of this synchronous detection circuit, characterized in that the computation portion is further configured that for the determination of the concentration of the gas for measurement the timing of a pulse-shape trigger signal synchronized with the wavelength scanning driving signal and output from the laser driving signal generation portion is taken as reference, and the expected timing of occurrence of the maximum value and the minimum value (B,D) of the gas absorption waveform relative to the timing of the pulse-shape trigger signal is determined in advance and saved, and at the time of measurement of gas concentration, the maximum value and minimum value (B,D) are measured from the output signal (Sb) of the synchronous detection circuit at the expected timing of occurrence of the maximum value and minimum value (B,D). a laser driving signal generation portion configured to combine a wavelength scanning driving signal that varies the emission wavelength of a laser element so as to scan the absorption wavelength of the gas for measurement and a high-frequency modulation signal to modulate the emission wavelength, and to output the result as a laser driving signal; a current control portion which converts the laser driving signal output from the laser driving signal generation portion into a current; and the laser element to which the current output from the current control portion is supplied; wherein the signal processing circuit is configured to detect, from the output signal of the light-receiving portion, a signal of a component at twice the frequency of the modulation signal modulating the emission wavelength, and measure the concentration of the gas for measurement; and wherein a synchronous detection circuit which detects the amplitude of the signal of the frequency-doubled component from the output signal of the light-receiving portion; and a computation portion configured to determine the concentration of the gas for measurement from the difference between a maximum value and a minimum value of a gas absorption waveform existing in the output signal (Sb) of this synchronous detection circuit, characterized in that the computation portion is further configured that for the determination of the concentration of the gas for measurement the timing of a pulse-shape trigger signal synchronized with the wavelength scanning driving signal and output from the laser driving signal generation portion is taken as reference, and the expected timing of occurrence of the maximum value and the minimum value (B,D) of the gas absorption waveform relative to the timing of the pulse-shape trigger signal is determined in advance and saved, and at the time of measurement of gas concentration, the maximum value and minimum value (B,D) are measured from the output signal (Sb) of the synchronous detection circuit at the expected timing of occurrence of the maximum value and minimum value (B,D).