A relay optical system includes a cemented lens in which a first lens, a second lens, and a third lens having are cemented. The first lens is a meniscus lens which is adjacent to the third lens, and a dispersion and a partial dispersion ratio differ for the first lens and the third lens. In a rectangular coordinate system in which a horizontal axis is set to be νdLA and a vertical axis is set to be θgFLA, when a straight line expressed by θgFLA=α×νdLA+βLA (where, α=−0.00163) is set, θgFLA and νdLA of medium of the first lens are included in an area determined by the following conditional expression (1) and conditional expression (2), and the following conditional expression (3) is satisfied: 0.67≤βLA  (1) νdLA