The present thermally assisted magnetic head has: a plasmon antenna; an optical wave guide having the plasmon antenna installed at the tip thereof; a diffraction grating which is disposed in or on the optical wave guide; and a laser element which is disposed at a position to irradiate laser beams onto the diffraction grating, and is composed of a photonic crystal surface emitting semiconductor layer. A laser light intensity distribution on the diffraction grating has at least two intensity peaks in the width direction of the optical wave guide. The two-dimensional form of the laser light intensity distribution on the diffraction grating is a ring or two ellipses.