A thermally-assisted magnetic recording head that includes a pole that generates a writing magnetic field, a waveguide through which light propagates, a plasmon generator that surface-evanescent-couples with the light propagating through the waveguide, wherein the plasmon generator includes a portion where a cross-sectional area gradually decreases as going toward a depth side from an air bearing surface when being observed from a cross section parallel to the air bearing surface. The volume of the plasmon generator can be decreased and an exposed area of a front surface on the air bearing surface can be increased. When a thermal expansion from the temperature increase occurs in the plasmon generator, a rate that the plasmon generator projects from the air bearing surface is suppressed to extremely low levels. Accordingly, a chronological degradation of output can be suppressed and thermally-assisted recording having a high and long-term reliability is achieved.