Projection optical system including movable lens groups and image display apparatus

A magnification optical system that enlarges an image of an object, the magnification optical system comprising:

• a first optical system including a plurality of lens groups;
• a second optical system including a curved mirror that reflects light received from the first optical system;
• and
• a focus structure that moves a part of the plurality of lens groups of the first optical system, wherein
• the plurality of lens groups includes, in order from an object side to an enlarged side:
• a first lens group,
• a second lens group having a positive power,
• a third lens group having a negative power, and
• a fourth lens group,
• the focus structure moves the third lens group and the fourth lens group, and does not move the first lens group and the curved mirror, to change an interval between the fourth lens group and the third lens group, and
• the focus structure further moves the second lens group.