In a laser surgical unit having a contact laser probe (1), a hydroxyl group (13) is included in the contact laser probe so that a laser beam is partially absorbed by the hydroxyl group (13) to heat the contact laser probe (1) for transmission to living tissue. Consequently, a coagulation layer is formed in the living tissue along with vaporization and incision. At least a part of the contact laser probe (1) is made of a material which contains the hydroxyl group (13) generally in an amount of between 0.5 and 10 ppm. Alternatively, the hydroxyl group (13) may be included only in a portion adjacent to a surface of a tip portion of the probe (1). As a further alternative, a coating film containing the hydroxyl group (13) may be attached to the tip of the contact laser probe (1). The laser beam preferably has a wavelength between 1.5 and 15 .mu.m. For example, use is made of an Er:YAG laser beam, a Ho:YAG laser beam, or a CO.sub.2 laser beam. The laser surgical unit of the above-mentioned structure is excellent in manipulatability, capable of safely and uniformly cutting living tissue, and capable of successively performing hemostasis.