A single-reflex camera comprising: a mirror box configured to house a mirror configured to deflect part of a light flux that has passed through an image-pickup optical system when the mirror is inserted into an optical path of the light flux; and a focus detecting unit that includes a condenser lens configured to condense a light flux deflected by the mirror, and provides focus detections using light condensed by the condenser lens and a phase difference method, wherein the mirror box further includes: a first opening, arranged to allow the light flux that has passed through the image-pickup optical system and a camera mount to enter the mirror box; a bottom plate arranged between the mirror and the focus detecting unit, the bottom plate including a front part that inclines towards an optical axis of the image-pickup optical system as it extends away from the first opening, wherein at least part of the condenser lens is located on a side of the optical axis of the image-pickup optical system with respect to a line extending from a bottom end of the first opening parallel to the optical axis of the image-pickup optical system wherein the bottom end of the first opening is the end of the first opening closest to the bottom plate, and characterized in that the bottom plate further includes: a plate-shaped center part positioned further away from the image-pickup optical system than the front part, wherein the center part is the closest part of the bottom plate to the optical axis; and a plate-shaped back part that inclines away from the optical axis as it extends away from the center part. a mirror box configured to house a mirror configured to deflect part of a light flux that has passed through an image-pickup optical system when the mirror is inserted into an optical path of the light flux; and a focus detecting unit that includes a condenser lens configured to condense a light flux deflected by the mirror, and provides focus detections using light condensed by the condenser lens and a phase difference method, wherein the mirror box further includes: a first opening, arranged to allow the light flux that has passed through the image-pickup optical system and a camera mount to enter the mirror box; a bottom plate arranged between the mirror and the focus detecting unit, the bottom plate including a front part that inclines towards an optical axis of the image-pickup optical system as it extends away from the first opening, wherein at least part of the condenser lens is located on a side of the optical axis of the image-pickup optical system with respect to a line extending from a bottom end of the first opening parallel to the optical axis of the image-pickup optical system wherein the bottom end of the first opening is the end of the first opening closest to the bottom plate, and characterized in that the bottom plate further includes: a plate-shaped center part positioned further away from the image-pickup optical system than the front part, wherein the center part is the closest part of the bottom plate to the optical axis; and a plate-shaped back part that inclines away from the optical axis as it extends away from the center part. a first opening, arranged to allow the light flux that has passed through the image-pickup optical system and a camera mount to enter the mirror box; a bottom plate arranged between the mirror and the focus detecting unit, the bottom plate including a front part that inclines towards an optical axis of the image-pickup optical system as it extends away from the first opening, wherein at least part of the condenser lens is located on a side of the optical axis of the image-pickup optical system with respect to a line extending from a bottom end of the first opening parallel to the optical axis of the image-pickup optical system wherein the bottom end of the first opening is the end of the first opening closest to the bottom plate, and characterized in that the bottom plate further includes: a plate-shaped center part positioned further away from the image-pickup optical system than the front part, wherein the center part is the closest part of the bottom plate to the optical axis; and a plate-shaped back part that inclines away from the optical axis as it extends away from the center part. a plate-shaped center part positioned further away from the image-pickup optical system than the front part, wherein the center part is the closest part of the bottom plate to the optical axis; and a plate-shaped back part that inclines away from the optical axis as it extends away from the center part.