To provide a heat transfer performance measuring instrument having a temperature sensor without forming the housing part of the temperature sensor to a measuring target and equipped with a mounting constitution of the temperature sensor on the measuring target.

The heat transfer performance measuring instrument 1 is equipped with the measuring target 2, which has a measuring sample body 21 having a heat transfer surface 23 made of an aluminum alloy extended material and has a rectangular parallelpiped outer shape and a rectangular plane and a plurality round holes for the flow channel 22 of a heating medium 9 formed thereto and having thinnest-walled part of 0.7 mm, a heat source device body 3 having a rectangular plane 32 made of oxygen free copper and the sheathed heater 36 of the heating source of the heating medium 9, a plurality of thermocouples 4 having a spherical temperature measuring contact point with a diameter of 0.42 mm and mounted on the heat transfer surface 23, a plurality of the inserts 5 made of a stainless steel material with an outer diameter of 0.5 mm inserted in the gap between the heat transfer surface 23 and a plane 32 and a greasy heat transfer material 6 inserted in the heat transfer surface 23 and the plane 32 and using a radiation silicone oil compound.