A light source device includes first and second light source units, a first polarization beam splitter, and a polarization conversion element. The first light source unit emits first linear polarization light in a first direction. The second light source unit is disposed facing the first light source unit, and emits the first linear polarization light in a second direction opposite to the first direction. The first linear polarization light emitted from the first light source unit is reflected by the first polarization beam splitter in a third direction perpendicular to the first and second directions. The first linear polarization light emitted from the second light source unit is reflected by the first polarization beam splitter in a fourth direction opposite to the third direction, is converted into the second linear polarization light by the polarization conversion element, and is reflected in the third direction.