Cartridge and image forming apparatus

A cartridge comprising:

• a container configured to accommodate developer;
• a light guide including an incident portion and an emergent portion, wherein the incident portion has a columnar shape with a center line as a center and guides light so that the light enters from outside of the cartridge into an inside of the container, and wherein the emergent portion guides the light so that the light entered into the inside of the container through the incident portion emerges toward outside of the cartridge;
• and
• a cover configured to partially cover the light guide and including an outer surface facing outside of the cartridge, an inner surface on a side opposite from the outer surface, a first opening through which an incident surface of the incident portion is exposed to outside of the cartridge, and a second opening through which an emergent surface of the emergent portion is exposed to outside of the cartridge,
• wherein, when a direction which is a direction of the centerline and which directs from an outer surface side toward an inner surface side of the cover is a first direction, a direction which crosses the first direction and in which the incident portion and the emergent portion are arranged is a second direction, and a direction crossing both the first direction and the second direction is a third direction, in a cross section perpendicular to the third direction:
• (i) the outer surface includes a recessed portion recessed toward a downstream side of the first direction between the incident portion and the emergent portion with respect to the second direction,
• (ii) a first end of a bottom of the recessed portion on an incident portion side with respect to the second direction is positioned on a side downstream with respect to the first direction of a second end of the bottom on an emergent portion side with respect to the second direction, and
• (iii) the bottom is curved so as to be recessed toward the downstream side of the first direction between the first end and the second end relative to an imaginary rectilinear line connecting the first end and the second end.