To achieve a solid-state laser element capable of outputting a high-power laser, in a planar waveguide type solid-state laser element that causes a plurality of fundamental laser beams to oscillate in a direction of an optic axis within a flat plate-like laser medium, and forms a waveguide structure in a thickness direction of the laser medium, which is a direction perpendicular to a principal surface of the flat plate-like laser medium, the laser medium is separated in a principal-surface width direction of the laser medium, which is a direction perpendicular to the direction of the optic axis and the thickness direction of the laser medium, by a groove extending in the direction of the optic axis within the laser medium.