A two-dimensional photonic crystal laser, including: a two-dimensional photonic crystal made of a plate-shaped member provided with a periodic arrangement of many identically-shaped modified refractive index areas having a refractive index different from that of the plate-shaped member; and an active layer provided on one side of the two-dimensional photonic crystal, wherein: the modified refractive index areas are arranged at lattice points of a lattice with a same period (a) at least in two directions; a shape of each modified refractive index area is such that a feedback strength is different with respect to directions of two primitive reciprocal lattice vectors of the lattice; the feedback strength being defined by a following formula: κ f = 1 S ∫ s ε r → exp − j G → 2 • r → d r → where, S represents an area of a unit cell of the lattice, ε(r) represents a permittivity distribution in the unit cell, G 2 represents a reciprocal lattice vector representing a second-order Bragg diffraction, j represents an imaginary unit, and an integral sign ∫ S signifies performing an area integration within the unit cell; the two-dimensional photonic crystal has a periodic structure of a supercell, as a unit, which contains a plurality of lattice points; and a sum of the feedback strengths by all modified refractive index areas in the supercell is identical in each direction of the two primitive reciprocal lattice vectors, characterised in that the period (a) of the lattice is equal to a wavelength of light in the two-dimensional photonic crystal, wherein the light is generated within the active layer. a two-dimensional photonic crystal made of a plate-shaped member provided with a periodic arrangement of many identically-shaped modified refractive index areas having a refractive index different from that of the plate-shaped member; and an active layer provided on one side of the two-dimensional photonic crystal, wherein: the modified refractive index areas are arranged at lattice points of a lattice with a same period (a) at least in two directions; a shape of each modified refractive index area is such that a feedback strength is different with respect to directions of two primitive reciprocal lattice vectors of the lattice; the feedback strength being defined by a following formula: κ f = 1 S ∫ s ε r → exp − j G → 2 • r → d r → where, S represents an area of a unit cell of the lattice, ε(r) represents a permittivity distribution in the unit cell, G 2 represents a reciprocal lattice vector representing a second-order Bragg diffraction, j represents an imaginary unit, and an integral sign ∫ S signifies performing an area integration within the unit cell; the two-dimensional photonic crystal has a periodic structure of a supercell, as a unit, which contains a plurality of lattice points; and a sum of the feedback strengths by all modified refractive index areas in the supercell is identical in each direction of the two primitive reciprocal lattice vectors, characterised in that the period (a) of the lattice is equal to a wavelength of light in the two-dimensional photonic crystal, wherein the light is generated within the active layer. the modified refractive index areas are arranged at lattice points of a lattice with a same period (a) at least in two directions; a shape of each modified refractive index area is such that a feedback strength is different with respect to directions of two primitive reciprocal lattice vectors of the lattice; the feedback strength being defined by a following formula: κ f = 1 S ∫ s ε r → exp − j G → 2 • r → d r → where, S represents an area of a unit cell of the lattice, ε(r) represents a permittivity distribution in the unit cell, G 2 represents a reciprocal lattice vector representing a second-order Bragg diffraction, j represents an imaginary unit, and an integral sign ∫ S signifies performing an area integration within the unit cell; the two-dimensional photonic crystal has a periodic structure of a supercell, as a unit, which contains a plurality of lattice points; and a sum of the feedback strengths by all modified refractive index areas in the supercell is identical in each direction of the two primitive reciprocal lattice vectors, characterised in that the period (a) of the lattice is equal to a wavelength of light in the two-dimensional photonic crystal, wherein the light is generated within the active layer.