A transmission type adaptive optical system comprising: a laser emission device configured to emit a laser beam; a partial reflection mirror configured to reflect a part of the laser beam as reflected light and transmit another part thereof as transmission light; a wavefront sensor configured to detect wavefront distortion of the reflected light and to generate and output a wavefront distortion signal indicating the wavefront distortion; a control device configured to generate and output a control signal to correct the wavefront distortion based on the wavefront distortion signal; a heating light source configured to generate and emit heating light that adjusts temperature distribution in an irradiated optical element based on the control signal; a transmission type adaptive optical element arranged on a light path between the laser emission device and the partial reflection mirror to transmit the laser beam and configured to correct a wavefront of the laser beam by a refraction index distribution adjusted by a temperature distribution occurred by irradiation of the heating light; and an irradiation optical system configured to irradiate a desired target with transmission light that is transmitted through the partial reflection mirror; wherein the heating light is an other laser beam having a wavelength different from the laser beam, wherein a first absorption rate of absorbing the laser beam by the transmission type adaptive optical element is smaller than a second absorption rate of absorbing the other laser beam by the transmission type adaptive optical element ; and characterised in that the transmission type adaptive optical element is fixed to the laser emission device . a laser emission device configured to emit a laser beam; a partial reflection mirror configured to reflect a part of the laser beam as reflected light and transmit another part thereof as transmission light; a wavefront sensor configured to detect wavefront distortion of the reflected light and to generate and output a wavefront distortion signal indicating the wavefront distortion; a control device configured to generate and output a control signal to correct the wavefront distortion based on the wavefront distortion signal; a heating light source configured to generate and emit heating light that adjusts temperature distribution in an irradiated optical element based on the control signal; a transmission type adaptive optical element arranged on a light path between the laser emission device and the partial reflection mirror to transmit the laser beam and configured to correct a wavefront of the laser beam by a refraction index distribution adjusted by a temperature distribution occurred by irradiation of the heating light; and an irradiation optical system configured to irradiate a desired target with transmission light that is transmitted through the partial reflection mirror; wherein the heating light is an other laser beam having a wavelength different from the laser beam, wherein a first absorption rate of absorbing the laser beam by the transmission type adaptive optical element is smaller than a second absorption rate of absorbing the other laser beam by the transmission type adaptive optical element ; and characterised in that the transmission type adaptive optical element is fixed to the laser emission device . <EOS>