Mirror unit and image capturing apparatus

A mirror unit that can decrease the wait time before distance measurement. The mirror unit includes a first mirror; a second mirror; a first mirror holder that holds the first mirror, is rotatable on a rotational axis arranged above an optical path of the incident light, is lowered to a first mirror-down position, and is raised to a first mirror-up position; and a second mirror holder that includes an auxiliary component and a mirror holding component holding the second mirror, is lowered to a second mirror-down position, and is raised to a second mirror-up position, wherein the auxiliary component is provided below the first mirror holder in the direction of the lowering, is rotatable on a rotational axis that is the same as or parallel to the rotational axis of the first mirror holder, and can be lowered independently of the first mirror holder, and the mirror holding component is engaged with the auxiliary component to be relatively rotatable around a rotational axis that is parallel to the rotational axis of the auxiliary component.