To more correctly identify types of liquid cartridges attached in a liquid ejecting apparatus to which a plurality of liquid cartridges different in type from each other are individually attached and detached.

A cartridge detecting device includes a light accumulation member 21 provided in the liquid cartridge 3, a luminance detector 19 which is set in an apparatus body 2 to detect a luminance of a light emitted from the light accumulation member 21 of the liquid cartridge 3 attached to an attachment part 5, a light emitting device 20 set in the apparatus body 2, and a control part 13 which identifies the type of the liquid cartridge 3 attached to the attachment part 5. The light accumulation member 21 varies in light accumulation characteristics according to the type of a corresponding liquid cartridge. The control part 13 applies the light to the light accumulation member 21 set in the liquid cartridge 3 by driving the light emitting device 20 when the liquid cartridge 3 is present at a predetermined position of the attachment part 5, thereby identifying the type of the liquid cartridge 2 on the basis of the luminance of the light, emitted from the light accumulation member 21 and detected by the luminance detector 19 after driving of the light emitting device 20.