Some methods have been proposed for knot making on a space where surgeon's hands can't reach such as on laparoscopic surgery. Even though, they have problems like as non-acceptable objects remaining on the body. To cope with these difficulties, this research has proposed a new knot making instrument, named as “Weld Forceps”, where the ends of the suture threads are melted and welded together by heating. As a result of trying the weld forceps for some bio tissue, there was a point-like burn. This report is to clear thermal characteristics between the weld forceps and the tissue, and to discuss about some heat insulator effect. At first, it is cleared as follows, as basic data ; thermal diffusivities of some tissues are almost same or a little less than that of water, and burn whitening of the tissue begins with temperature rising to about 50°C. Then, the temperature characteristics were measured for the heat transfer system of the weld forceps, heat insulator and bio tissue in 60-second interval heating. And we got as follows. On the heating power that is sufficient for welding, the maximum temperature of the bio tissue was about 45°C, and was under 40°C with heat insulator (Epoxy resin, 0.3 mm thickness). In consequence, it is also discussed about the reasons why the point-like burn could occur.