An optical resonator includes a first substrate and a second substrate which face each other, the first substrate having a flat main surface on which a first reflective mirror is provided and the second substrate having a concave portion on which a second reflective mirror is provided and a flat portion which surrounds the concave portion. The main surface of the first substrate and the flat portion of the second substrate are bondable. In addition, a laser oscillator includes a solid-state laser medium and a substrate, the solid-state laser medium having a main surface on which a first reflective mirror is provided and the substrate having a concave portion on which a second mirror is provided and a flat portion which surrounds the concave portion. The first and the second reflective mirrors serve as a laser resonator.