A semiconductor light emitting device comprising: a semiconductor light emitting element; a mount that is provided with the semiconductor light emitting element mounted thereon; and a cap that includes: a transparent member that allows emission light from the semiconductor light emitting element to pass therethrough; and a cap member that supports the transparent member, wherein the semiconductor light emitting element is sealed by the mount and the cap, wherein the cap member has an inclined portion forming a penetrating opening, which is formed in such a manner that the penetrating opening is getting wider toward the outside from the inside where the semiconductor light emitting element is mounted, said penetrating opening being bounded by a single inclined wall surface, said penetrating opening having a light entering portion corresponding to the opening end of the penetrating opening where an emission light from the semiconductor element can enter said penetrating opening, wherein a bottom surface of said transparent member is positioned higher than said light entering portion so that a space is formed between the bottom surface of the transparent member and said light entering portion, wherein part of said inclined wall surface supports a peripheral part of the bottom surface of said transparent member, and the transparent member contains a wavelength conversion material that absorbs the emission light from the semiconductor light emitting element and converts the wavelength of the emission light, or a light scattering material that scatters the emission light from the semiconductor light emitting element, and the semiconductor light emitting element is a semiconductor laser diode. a semiconductor light emitting element; a mount that is provided with the semiconductor light emitting element mounted thereon; and a cap that includes: a transparent member that allows emission light from the semiconductor light emitting element to pass therethrough; and a cap member that supports the transparent member, wherein the semiconductor light emitting element is sealed by the mount and the cap, wherein the cap member has an inclined portion forming a penetrating opening, which is formed in such a manner that the penetrating opening is getting wider toward the outside from the inside where the semiconductor light emitting element is mounted, said penetrating opening being bounded by a single inclined wall surface, said penetrating opening having a light entering portion corresponding to the opening end of the penetrating opening where an emission light from the semiconductor element can enter said penetrating opening, wherein a bottom surface of said transparent member is positioned higher than said light entering portion so that a space is formed between the bottom surface of the transparent member and said light entering portion, wherein part of said inclined wall surface supports a peripheral part of the bottom surface of said transparent member, and the transparent member contains a wavelength conversion material that absorbs the emission light from the semiconductor light emitting element and converts the wavelength of the emission light, or a light scattering material that scatters the emission light from the semiconductor light emitting element, and the semiconductor light emitting element is a semiconductor laser diode.