Provided is a thermal-assisted-magnetic-recording head capable of irradiating a magnetic recording medium with light with a spot size reduced on the submicron order with high utilization efficiency. A spot size converter 13 for guiding light emitted from an optical source 4 into a magnetic head is provided at a position adjacent to a magnetic main pole 19 in the magnetic head. In the spot size converter 13, a cover layer 15 having a lower refractive index than those of a core 14 and a clad material 24 is formed between the core 14 and the clad 15 and has a shape composed of a shape substantially rectangular in a light traveling direction and a taper shape having a width increasing toward the bottom surface of the magnetic head.