A light emitting device comprising: a first conductivity type semiconductor layer; an active layer to generate a light on the first conductivity type semiconductor layer; a second conductivity type semiconductor layer on the active layer; a transparent electrode layer on the second conductivity type semiconductor layer; and a multiple thin film mirror on the transparent electrode layer, the multiple thin film mirror being formed by repeatedly stacking a first thin film layer having a first refractive index and a second thin film layer having a second refractive index different from the first refractive index, wherein the phase shift occurring when the light is reflected from the multiple thin film mirror is 0, wherein the multiple thin film mirror reflects the light through the total reflection according to the incident angle of the light, and wherein the first thin film layer is positioned at the lowest layer of the multiple thin film mirror, the refractive index of the first thin film layer is higher or lower than the refractive index of the second thin film layer and the refractive index of the transparent electrode layer, characterized in that the second conductivity type semiconductor layer has a thickness satisfying following equation 1: 2 ⋅ Φ 1 + Φ 2 = N ⋅ 2 π ± Δ, 0 ≤ Δ ≤ π / 2,, wherein Φ1 is a phase shift occurring when a light, which travels in a vertical direction, passes through the second conductivity type semiconductor layer and is expressed as Φ1= 2πnd/λ (n is a refractive index of the light, λ is a wavelength of the light, and d is a thickness of the second conductivity type semiconductor layer), Φ2 is a phase shift occurring when the light is reflected from the transparent electrode layer, and N is a natural number, wherein the phase shift Φ2 occurring when the light is reflected from the transparent electrode layer is 0, and wherein the thickness(d) of the second conductivity type semiconductor layer satisfying the constructive interference condition is expressed as equation 2 below: d = λ / 4 π n ⋅ N ⋅ 2 π ± Δ, 0 ≤ Δ ≤ π / 2. a first conductivity type semiconductor layer; an active layer to generate a light on the first conductivity type semiconductor layer; a second conductivity type semiconductor layer on the active layer; a transparent electrode layer on the second conductivity type semiconductor layer; and a multiple thin film mirror on the transparent electrode layer, the multiple thin film mirror being formed by repeatedly stacking a first thin film layer having a first refractive index and a second thin film layer having a second refractive index different from the first refractive index, wherein the phase shift occurring when the light is reflected from the multiple thin film mirror is 0, wherein the multiple thin film mirror reflects the light through the total reflection according to the incident angle of the light, and wherein the first thin film layer is positioned at the lowest layer of the multiple thin film mirror, the refractive index of the first thin film layer is higher or lower than the refractive index of the second thin film layer and the refractive index of the transparent electrode layer, characterized in that the second conductivity type semiconductor layer has a thickness satisfying following equation 1: 2 ⋅ Φ 1 + Φ 2 = N ⋅ 2 π ± Δ, 0 ≤ Δ ≤ π / 2,, wherein Φ1 is a phase shift occurring when a light, which travels in a vertical direction, passes through the second conductivity type semiconductor layer and is expressed as Φ1= 2πnd/λ (n is a refractive index of the light, λ is a wavelength of the light, and d is a thickness of the second conductivity type semiconductor layer), Φ2 is a phase shift occurring when the light is reflected from the transparent electrode layer, and N is a natural number, wherein the phase shift Φ2 occurring when the light is reflected from the transparent electrode layer is 0, and wherein the thickness(d) of the second conductivity type semiconductor layer satisfying the constructive interference condition is expressed as equation 2 below: d = λ / 4 π n ⋅ N ⋅ 2 π ± Δ, 0 ≤ Δ ≤ π / 2., wherein Φ1 is a phase shift occurring when a light, which travels in a vertical direction, passes through the second conductivity type semiconductor layer and is expressed as Φ1= 2πnd/λ (n is a refractive index of the light, λ is a wavelength of the light, and d is a thickness of the second conductivity type semiconductor layer), Φ2 is a phase shift occurring when the light is reflected from the transparent electrode layer, and N is a natural number, wherein the phase shift Φ2 occurring when the light is reflected from the transparent electrode layer is 0, and wherein the thickness(d) of the second conductivity type semiconductor layer satisfying the constructive interference condition is expressed as equation 2 below: d = λ / 4 π n ⋅ N ⋅ 2 π ± Δ, 0 ≤ Δ ≤ π / 2.