A constituent concentration measuring apparatus characterized by comprising: light generating means (301, 302) adapted to generate two light beams (1a, 1b) having different wavelengths; light modulation means adapted to electrically intensity-modulate each of the two light beams (1a, 1b) having the mutually different wavelengths using signals having the same frequency and reverse phases; light outgoing means (301, 302) adapted to output the two intensity-modulated light beams (1a, 1b) having the mutually different wavelengths toward a test subject; acoustic wave detection means adapted to detect an acoustic wave emitted from the test subject by the outputted light; frequency sweep means adapted to sweep a modulation frequency, the light generated by said light generating means (301, 302) being modulated in the modulation frequency; and integration means adapted to integrate the acoustic wave in a swept modulation frequency range, the acoustic wave being detected by said acoustic wave detection means, constituent concentration computation means adapted to compute a constituent concentration of a liquid from the acoustic wave integrated by said integration means, the constituent being set as a measuring object in the test subject; wherein the modulation means is adapted to electrically intensity-modulate each of said two light beams (1a, 1b) having the mutually different wavelengths using a signal from said frequency sweep means and with mutually reverse modulation phases, and the constituent concentration computation means is adapted to divide pressure of the acoustic wave, which is emitted by irradiating the two light beams (1a, 1b) having the mutually different wavelengths to the test subject, by pressure of the acoustic wave which is emitted when one of the two light beams (1a, 1b) is set to zero power. light generating means (301, 302) adapted to generate two light beams (1a, 1b) having different wavelengths; light modulation means adapted to electrically intensity-modulate each of the two light beams (1a, 1b) having the mutually different wavelengths using signals having the same frequency and reverse phases; light outgoing means (301, 302) adapted to output the two intensity-modulated light beams (1a, 1b) having the mutually different wavelengths toward a test subject; acoustic wave detection means adapted to detect an acoustic wave emitted from the test subject by the outputted light; frequency sweep means adapted to sweep a modulation frequency, the light generated by said light generating means (301, 302) being modulated in the modulation frequency; and integration means adapted to integrate the acoustic wave in a swept modulation frequency range, the acoustic wave being detected by said acoustic wave detection means, constituent concentration computation means adapted to compute a constituent concentration of a liquid from the acoustic wave integrated by said integration means, the constituent being set as a measuring object in the test subject; wherein the modulation means is adapted to electrically intensity-modulate each of said two light beams (1a, 1b) having the mutually different wavelengths using a signal from said frequency sweep means and with mutually reverse modulation phases, and the constituent concentration computation means is adapted to divide pressure of the acoustic wave, which is emitted by irradiating the two light beams (1a, 1b) having the mutually different wavelengths to the test subject, by pressure of the acoustic wave which is emitted when one of the two light beams (1a, 1b) is set to zero power.