An external resonator laser type light emitting system comprising a light source oscillating a semiconductor laser light by itself and a grating device providing an external resonator with said light source, said light emitting system emitting an external resonator laser light in single longitudinal mode; said light emitting system operating in composite resonator mode oscillating both of said external resonator laser light and said semiconductor laser light; wherein said light source comprises an active layer oscillating said semiconductor laser light; wherein said grating device comprises an optical waveguide comprising an incident face to which said semiconductor laser light is incident and an emitting face of emitting an emitting light having a desired wavelength, a Bragg grating formed in said optical waveguide, and a propagating portion provided between said incident face and said Bragg grating; wherein the following formulas to are satisfied, wherein said light source and said grating device are optically connected to each other directly; wherein said external resonator is constituted between said Bragg grating and an outer side end face of said active layer on the opposite side to an emitting face of said active layer; and wherein a length between said outer side end face of said active layer and an emitting side end point of said Bragg grating is 910 μm or smaller, wherein said optical waveguide comprises a core (30, 30A); wherein a cross section of said core is of a convex shape, and said light source comprises a reflection layer formed on said emitting face of said active layer on the side of said grating device, Δ λ G ≧ 0.8 nm L b ≦ 500 μm L a ≦ 500 μm n b ≧ 1.8 | d λ G dT − d λ TM dT | ≦ 0.03 nm / ° C where Δλ G represents a full width at half maximum of a peak of a Bragg reflectance in said formula, L b represents a length of said Bragg grating in said formula, L a represents a length of said active layer in said formula, n b represents a refractive index of a material forming said Bragg grating in said formula, and dλ G /dT represents a temperature coefficient of a Bragg wavelength, and dλ TM /dT represents a temperature coefficient of a wavelength satisfying a phase condition of said external resonator in said formula. said light emitting system operating in composite resonator mode oscillating both of said external resonator laser light and said semiconductor laser light; wherein said light source comprises an active layer oscillating said semiconductor laser light; wherein said grating device comprises an optical waveguide comprising an incident face to which said semiconductor laser light is incident and an emitting face of emitting an emitting light having a desired wavelength, a Bragg grating formed in said optical waveguide, and a propagating portion provided between said incident face and said Bragg grating; wherein the following formulas to are satisfied, wherein said light source and said grating device are optically connected to each other directly; wherein said external resonator is constituted between said Bragg grating and an outer side end face of said active layer on the opposite side to an emitting face of said active layer; and wherein a length between said outer side end face of said active layer and an emitting side end point of said Bragg grating is 910 μm or smaller, wherein said optical waveguide comprises a core (30, 30A); wherein a cross section of said core is of a convex shape, and said light source comprises a reflection layer formed on said emitting face of said active layer on the side of said grating device, Δ λ G ≧ 0.8 nm L b ≦ 500 μm L a ≦ 500 μm n b ≧ 1.8 | d λ G dT − d λ TM dT | ≦ 0.03 nm / ° C where Δλ G represents a full width at half maximum of a peak of a Bragg reflectance in said formula, L b represents a length of said Bragg grating in said formula, L a represents a length of said active layer in said formula, n b represents a refractive index of a material forming said Bragg grating in said formula, and dλ G /dT represents a temperature coefficient of a Bragg wavelength, and dλ TM /dT represents a temperature coefficient of a wavelength satisfying a phase condition of said external resonator in said formula. where Δλ G represents a full width at half maximum of a peak of a Bragg reflectance in said formula, L b represents a length of said Bragg grating in said formula, L a represents a length of said active layer in said formula, n b represents a refractive index of a material forming said Bragg grating in said formula, and dλ G /dT represents a temperature coefficient of a Bragg wavelength, and dλ TM /dT represents a temperature coefficient of a wavelength satisfying a phase condition of said external resonator in said formula.