Provided is a projection optical system (10) that projects a first image (IM0) on a reduction side (2) toward an enlargement side (3), the projection optical system including: a first optical system (11) including a plurality of lenses; and a second optical system (12) including a first reflective face (13) located on the enlargement side and having a positive refractive power. The first optical system renders a first intermediate image (IM1), formed inside the first optical system by light incident from the reduction side, into a second intermediate image (IM2) on the enlargement side with respect to the first optical system. The first optical system includes: a first refractive optical system (15) including a first optical axis (21), which is shifted in a first direction (31) relative to center light (20) of the first image; and a second refractive optical system (16) including a second optical axis (22), which is shifted in the first direction relative to the first optical axis (21).