A semiconductor laser device, comprising: - a first conductivity type cladding layer having a refractive index n c1 ; - a first conductivity type side optical guide layer which is undoped; - an active layer ; - a second conductivity type side optical guide layer which is undoped; - a second conductivity type cladding layer having a refractive index n c2 ; and - a resonator in which laser light travels back and forth, wherein: - the above layers are laminated in that order on a semiconductor substrate of a first conductivity type, - an oscillation wavelength is λ; - a structure of the device is such that a first-order or higher-order mode is allowed in a lamination direction (y) in a cross section perpendicular to an optical axis direction (z) of the resonator, - a structure of the device is a broad area structure in which a first-order or higher-order mode is allowed in a direction (x) perpendicular to the optical axis direction (z) of the resonator and the lamination direction (y), - the broad area structure is formed with a ridge shape having a ridge region (I) and cladding regions (II, IIa) on both sides of the ridge region (I); - a first conductivity type low refractive index layer having a thickness of d 1 and a refractive index n 1 lower than n c1 is provided between the first conductivity type side optical guide layer and the first conductivity type cladding layer or inside the first conductivity type cladding layer , - a second conductivity type low refractive index layer having a thickness of d 2 and a refractive index n 2 lower than n c2 is provided between the second conductivity type side optical guide layer and the second conductivity type cladding layer or inside the second conductivity type cladding layer , and - a relationship 2 π λ n c 2 2 − n 2 2 d 2 2 > 2 π λ n c 1 2 − n 1 2 d 1 2 is satisfied. - a first conductivity type cladding layer having a refractive index n c1 ; - a first conductivity type side optical guide layer which is undoped; - an active layer ; - a second conductivity type side optical guide layer which is undoped; - a second conductivity type cladding layer having a refractive index n c2 ; and - a resonator in which laser light travels back and forth, - the above layers are laminated in that order on a semiconductor substrate of a first conductivity type, - an oscillation wavelength is λ; - a structure of the device is such that a first-order or higher-order mode is allowed in a lamination direction (y) in a cross section perpendicular to an optical axis direction (z) of the resonator, - a structure of the device is a broad area structure in which a first-order or higher-order mode is allowed in a direction (x) perpendicular to the optical axis direction (z) of the resonator and the lamination direction (y), - the broad area structure is formed with a ridge shape having a ridge region (I) and cladding regions (II, IIa) on both sides of the ridge region (I); - a first conductivity type low refractive index layer having a thickness of d 1 and a refractive index n 1 lower than n c1 is provided between the first conductivity type side optical guide layer and the first conductivity type cladding layer or inside the first conductivity type cladding layer , - a second conductivity type low refractive index layer having a thickness of d 2 and a refractive index n 2 lower than n c2 is provided between the second conductivity type side optical guide layer and the second conductivity type cladding layer or inside the second conductivity type cladding layer , and - a relationship 2 π λ n c 2 2 − n 2 2 d 2 2 > 2 π λ n c 1 2 − n 1 2 d 1 2 is satisfied. <EOS>