An optical scanning device comprising a waveguide array including a plurality of waveguides (1, 10) arranged in a first direction, wherein each of the plurality of waveguides (1, 10) includes: an optical waveguide layer that propagates light supplied to the waveguide, in a second direction intersecting the first direction; a first mirror extending in the second direction and having a first reflecting surface; and a second mirror extending in the second direction and having a second reflecting surface that faces the first reflecting surface of the first mirror, the width of the second mirror in the first direction is larger than the width of the optical waveguide layer in the first direction, wherein, in each of the plurality of waveguides (1, 10), the optical waveguide layer is located between the first mirror and the second mirror and has a variable thickness and/or a variable refractive index for the light, wherein the first mirror has a higher light transmittance than the second mirror and allows part of the light propagating through the optical waveguide layer to pass through and be emitted, and wherein the refractive index of the optical waveguide layer and/or the thickness of the optical waveguide layer is changed to thereby change an emission direction of the part of the light characterized in that the width of the first mirror in the first direction is larger than the width of the optical waveguide layer in the first direction. wherein each of the plurality of waveguides (1, 10) includes: an optical waveguide layer that propagates light supplied to the waveguide, in a second direction intersecting the first direction; a first mirror extending in the second direction and having a first reflecting surface; and a second mirror extending in the second direction and having a second reflecting surface that faces the first reflecting surface of the first mirror, the width of the second mirror in the first direction is larger than the width of the optical waveguide layer in the first direction, an optical waveguide layer that propagates light supplied to the waveguide, in a second direction intersecting the first direction; a first mirror extending in the second direction and having a first reflecting surface; and a second mirror extending in the second direction and having a second reflecting surface that faces the first reflecting surface of the first mirror, the width of the second mirror in the first direction is larger than the width of the optical waveguide layer in the first direction, wherein, in each of the plurality of waveguides (1, 10), the optical waveguide layer is located between the first mirror and the second mirror and has a variable thickness and/or a variable refractive index for the light, wherein the first mirror has a higher light transmittance than the second mirror and allows part of the light propagating through the optical waveguide layer to pass through and be emitted, and wherein the refractive index of the optical waveguide layer and/or the thickness of the optical waveguide layer is changed to thereby change an emission direction of the part of the light characterized in that the width of the first mirror in the first direction is larger than the width of the optical waveguide layer in the first direction.