A seat heater that is a seat including: a planer heating element that has a plurality of electric heating wires on its upper surface and that includes a fiber layer; a cushion member that locates over a lower surface of the planer heating element; and a skin that locates above the planer heating element, wherein the planer heating element has, in voids of the fiber layer, a silica aerogel that is a silica porous body having pores with a mean pore diameter of 10 nm to 68 nm.