A heat generating body (20) has a first electrode (26) and a second electrode (28) arranged opposed to each other, and also has a mesh-like electrically conductive membrane (mesh-like pattern (24)) mounted in a curved surface shape between the first electrode (26) and the second electrode (28). The first electrode (26) and the second electrode (28) are arranged so as to satisfy the relationship of (Lmax - Lmin)/((Lmax + Lmin)/2) = 0.375, where Lmin is a minimum value of the distance between two opposite points which are on the first and second electrodes (26, 28) and on the electrically conductive membrane and Lmax is a maximum value of the distance.
