A light irradiation device for emitting light of two or more components by laser light, to an outside, comprising: a laser light source which emits the laser light; a diffusion optical path changing member configured to convert a first color component of the laser light into diffusion light, remove coherency and change an optical path of the first color component; a phosphor configured to generate fluorescence of a second color component different from the first color component based on the first color component of the laser light, and change an optical path of the second color component; and an optical path switching member, between the laser light source and the diffusion optical path changing member, configured to switch between a first optical path for emitting the first color component and a second optical path for emitting the second color component, wherein the first optical path is changed by the diffusion optical path changing member to emit the first color component to the outside, and the second optical path component is changed by the phosphor to emit the second color component to the outside; wherein the diffusion optical path changing member includes a reflection diffusion member configured to convert the laser light emitted by the laser light source into diffusion light and reflect the laser light, wherein the reflection diffusion member has a structure in which a light transmission diffusion layer is formed on the planar light reflection surface, and is arranged so that the laser light passes through the light transmission diffusion layer and is reflected at a light reflection surface and thereafter passes through the light transmission diffusion layer again; wherein at a destination of any laser light emitted toward the diffusion optical path changing member in the case that it goes straight at the light diffusion position, a laser light leaking prevention means (19; 22) for preventing the laser light from leaking to the outside remaining in a non-diffused state is arranged. a laser light source which emits the laser light; a diffusion optical path changing member configured to convert a first color component of the laser light into diffusion light, remove coherency and change an optical path of the first color component; a phosphor configured to generate fluorescence of a second color component different from the first color component based on the first color component of the laser light, and change an optical path of the second color component; and an optical path switching member, between the laser light source and the diffusion optical path changing member, configured to switch between a first optical path for emitting the first color component and a second optical path for emitting the second color component, wherein the first optical path is changed by the diffusion optical path changing member to emit the first color component to the outside, and the second optical path component is changed by the phosphor to emit the second color component to the outside; wherein the diffusion optical path changing member includes a reflection diffusion member configured to convert the laser light emitted by the laser light source into diffusion light and reflect the laser light, wherein the reflection diffusion member has a structure in which a light transmission diffusion layer is formed on the planar light reflection surface, and is arranged so that the laser light passes through the light transmission diffusion layer and is reflected at a light reflection surface and thereafter passes through the light transmission diffusion layer again; wherein at a destination of any laser light emitted toward the diffusion optical path changing member in the case that it goes straight at the light diffusion position, a laser light leaking prevention means (19; 22) for preventing the laser light from leaking to the outside remaining in a non-diffused state is arranged.