PURPOSE: To efficiently and uniformly heat a groove part in a body to be heated with low electric power in a device with simple constitution and an easy operation.

CONSTITUTION: In a device 1 for heating the groove part 15 of the body 12 to be heated, (A) a unit conductor 5 composed by interposing an electric insulator (insulating plate 4) between a first conductor 2 and a second conductor 3, (B) a first contact electrode 7 connected to the first conductor 2 and arranged while abutted on one side part of the opening part 14 of the groove part 15, (C) a second contact electrode 8 connected to the second conductor 3 and arranged while abutted on the other side part of the opening part 14 of the groove part 15, (D) driving mechanism arranged while abutted on the one side part and the other side part of the opening part 14 of the first connecting electrode 7 and the second connecting electrode 8, respectively and (E) a high frequency power source 11 connected between the first conductor 2 and the second conductor 3 are arranged. By abutting the first and the second contacting electrodes 7, 8 on both sides of the opening part 14, thereby making directly the high frequency current flow to the groove surface 15a of the groove part 15, the groove part 15 is heated.