An ink cartridge determination system includes a cartridge mounting portion, an optical sensor positioned at the cartridge mounting portion, at least one ink cartridge configured to be inserted into the cartridge mounting portion, and a determiner. The optical sensor includes a light-emitting element and a light-receiving element. The optical sensor is configured to selectively output a first signal and a second signal based on an intensity of the light received by the light-receiving element. The at least one ink cartridge includes a first light altering portion, a second light altering portion, and a light passing portion, which are configured to sequentially intersect a optical path of the optical sensor when the at least one ink cartridge is inserted into the cartridge mounting portion, and the determiner is configured to determine a type of the at least one ink cartridge based on a time profile of a signal outputted from the optical sensor.