Abstract: A medical laser treatment device comprising a laser generation source and a laser handpiece which comprises a light-guiding fiber used to guide a laser beam irradiated from the laser generation source, a probe for guiding the laser beam having been guided by the fiber to an object to be irradiated, at least two independent air supply passages and at least one water supply passage, the laser handpiece being adapted such that the emission end of the light-guiding fiber is airtightly isolated from the incident end of the probe via a light-guiding shield plate to make the internal section of the light-guiding fiber airtight, to cool the emission end of the light-guiding fiber using dry gas supplied from the first air supply passage and to cool the incident end of the probe using gas supplied from the second air supply passage, and being also arranged such that water supplied from the water supply passage is blown out from the peripheral section of the leading end of the probe, thereby preventing the emission end