The observation optical system introduces light from a first display element and light from a second display element to an exit pupil to present an enlarged combined image of first and second original images. The optical system includes a first optical element allowing the light from the first display element to enter thereinto, a second optical element allowing the light from the second display element to enter thereinto, and a third optical element. The optical system introduces a first light component from a first display area in the second display element to the exit pupil through the second optical element and at least the first optical element, and introduces a second light component from a second display area in the second display element to the exit pupil through the second and third optical elements, not through the first optical element.