Image forming apparatus having main assembly and including detection of remaining toner in mountable cartridge

An image forming apparatus comprising:

• an apparatus main body;
• and
• a cartridge mountable to and demountable from the apparatus main body and provided with an accommodating portion configured to accommodate a developer,
• wherein the apparatus main body includes:
• a frame provided with an opening;
• an urging member;
• a detecting unit (i) which includes a light emitting portion configured to emit light, a light receiving portion configured to receive the light emitted by the light emitting portion, and a pressed portion and (ii) which is configured to output a detection signal depending on a light receiving amount of the light received by the light receiving portion, wherein the detecting unit is provided movably relative to the frame between a first position and a second position, and is positioned in the first position by an urging force of the urging member, and wherein the detecting unit is moved from the first position to the second position against the urging force of the urging member by the pressed portion being pressed;
• and
• a shielding member provided movably relative to both the frame and the detecting unit between a third position and a fourth position,
• wherein the cartridge includes a light guiding member including a first light guiding portion configured to guide the light from the light emitting portion to an inside space of the accommodating portion and a second light guiding portion configured to guide the light passed through the inside space of the accommodating portion,
• wherein in a state in which the cartridge is not mounted to the apparatus main body, the detecting unit is positioned in the first position and the shielding member is positioned in the third position,
• wherein in a state in which the cartridge is mounted to the apparatus main body, the detecting unit is positioned in the second position and the shielding member is positioned in the fourth position,
• wherein when the detecting unit is positioned in the first position and the shielding member is positioned in the third position, in a case in which the detecting unit is viewed in an optical axis direction of the light emitting portion, at least one of at least a part of the light emitting portion and at least a part of the light receiving portion is positioned inside the opening, and the light emitting portion and the light receiving portion are shielded by the shielding member, and
• wherein when the detecting unit is positioned in the second position and the shielding member is positioned in the fourth position, both the light emitting portion and the light receiving portion are positioned inside the opening and are not shielded by the shielding member such that the light emitting portion opposes the first light guiding portion through the opening, and the light receiving portion opposes the second light guiding portion through the opening.