Evaporator for fuel cell

An evaporator (200) for a fuel cell includes a box (300) provided with an evaporating chamber (301) and a filling (503) formed of a plurality of evaporation promoting materials (500). Each of the evaporation promoting materials (500) formed with ceramics as base material is provided with spherical form. The box (300) is provided with a bottom wall (331), a side wall (332), and a corner wall (333) connecting the bottom wall (331) and the side wall (332) in an intersecting state. A curvature radius R1 at an inner surface (333i) of the corner wall (333), the inner surface (333i) facing the evaporating chamber (301), is larger relative to a curvature radius R2 of the evaporation promoting material (500). In other words, a relation of R1 > R2 holds.