Development cartridge and image forming apparatus

An image forming apparatus, in which a plurality of developing cartridges, different in the type of the toner they hold, can be removably installed, comprises:

• a plurality of developing cartridge slots in which said plurality of developing cartridges are correspondingly installed, each of the plurality of developing cartridges comprising:
• a toner carrying member for carrying toner to a developing station at which an electrostatic image formed on an image bearing member is developed with the toner;
• a toner accommodating portion for accommodating the toner to be supplied to said toner carrying member;
• a developing-cartridge engaging portion, the shape of which is different depending on the type of the toner it contains, and which is engageable with a main-assembly engaging portion of one of two or more developing cartridge slots provided in a main assembly side of the image forming apparatus;
• and a light transmitting portion disposed within said developing-cartridge engaging portion to transmit the light to be detected by a detecting means provided on the main assembly side of the image forming apparatus to detect the amount of the toner within said toner accommodating portion;
• and
• means for detecting the amount of the toner in said toner accommodating portion with the use of light;
• wherein said plurality of developing cartridge slots comprise the main-assembly engaging portion capable of engaging with the developing-cartridge engaging portion of the developing cartridge which each developing cartridge slot accepts, and wherein the main-assembly engaging portion of each developing cartridge slot is different in shape depending on the shape of the developing-cartridge engaging portion of the developing cartridge which the developing cartridge slot accepts, and
• wherein said detecting means comprises a light transmitting portion through which the toner detection light is allowed to pass, and wherein said light transmitting portion is in said main-assembly engaging portion of the developing cartridge slot.