To provide a polarization conversion element that is compact and has high light utilization efficiency, and a projection device using the polarization conversion element.

A polarization conversion element (10) for polarizing and separating the light emitted from a light source, includes a polarization separation surface (11) that transmits a polarizing component in a predetermined direction and reflects a polarizing component in a direction nearly perpendicular to the predetermined direction, and a reflection surface (12) that reflects the polarized light reflected on the polarization separation surface (11), toward the polarization separation surface (11). The polarization separation surface (11) has a curved surface shape for turning the reflected polarized light toward the reflection surface (12).