A light source device is equipped with a highly directional point light source, a light source installation part having a prescribed area where the point light source is installed, and a lateral reflection part that is vertically arranged to a prescribed height from the periphery of the light source installation part. The lateral reflection part is formed with a light-transmitting reflector plate that has a reflection/transmission pattern and is provided with multiple reflection/transmission parts for reflecting and at least partially transmitting light. In the reflection/transmission pattern, multiple virtual radial lines are drawn from the light source to the light-transmitting reflector plate surface at prescribed angles, and for reflection/transmission parts (Di,j) present on the radial lines that are at the same distance from the point light source, the reflectivity and transmissivity are denoted as Re1 and Tr1 when the reflection/transmission part is on a radial line at a narrow viewing angle to the point light source, and when the reflection/transmission part is on a radial line at a wide viewing angle to the point light source, the reflectivity and transmissivity are denoted as Re2 and Tr2. The relationship therebetween is set as follows: Re1>Re2 and Tr1.