To improve a degree of generation of frictional heat with respect to fluid caused by heating of the fluid even in a fluid heating gap 20a between adjacent faces of rotating bodies 12, 13 other than a fluid heating passage 20 of each of the rotating bodies 12, 13, and thus, enhance heating efficiency.

The plurality of rotating bodies 12, 13 rotatably supported within a case 1 including a fluid supply port 22 and a fluid discharge port 23 are juxtaposed. The fluid heating passages 20 are provided between outer peripheral faces 18, 19 of the rotating bodies 12, 13 adjacent to each other and relatively displaced and inner peripheral faces 10, 11 of the case 1. The outer peripheral faces 18, 19 of both rotating bodies 12, 13 adjacent to each other include the adjacent faces adjacent to each other leaving the fluid heating gap 20a and relatively displaced. Fluid supplied to the fluid supply port 22 is made to pass through the fluid heating passages 20 and the fluid heating gap 20a and is discharged from the fluid discharge port 23.