Optical system and projector

An optical system comprising:

• a first optical element;
• and
• a lens arranged at an enlargement side of the first optical element, wherein
• the first optical element has a first transmission surface, a first reflecting surface arranged at a reduction side of the first transmission surface, and a second transmission surface arranged at the reduction side of the first reflecting surface,
• the first transmission surface has positive power,
• light passing between the first transmission surface and the first reflecting surface includes peripheral light tilted in a direction of getting away from an enlargement-side conjugated plane as coming closer to the first transmission surface,
• the peripheral light is tilted in a direction of getting away from the enlargement-side conjugated plane as getting away from the first transmission surface between the first transmission surface and the lens, and
• the peripheral light is tilted in a direction of coming closer to the enlargement-side conjugated plane as getting away from the lens between the lens and the enlargement-side conjugated plane.