A determining system comprising: a cartridge-mounting portion in which a printing fluid cartridge is mountable, the printing fluid cartridge including a storage and an identification portion, the storage storing type information indicating a type of the printing fluid cartridge, the identification portion having a unique light transmission status differing depending on the type of the printing fluid cartridge; a photosensor disposed at the cartridge-mounting portion, the photosensor being configured to detect the unique light transmission status of the identification portion and output a signal differing depending on the detected unique light transmission status; and a controller configured to perform: (a) reading the type information from the storage of the printing fluid cartridge that is in a mounted state where the printing fluid cartridge is mounted in the cartridge-mounting portion, characterized in that the controller is further configured to perform: (b) determining the type of the printing fluid cartridge on the basis of both the read type information and the signal outputted from the photosensor (c) determining whether or not the type of the printing fluid cartridge determined on the basis of the read type information matches the type of the printing fluid cartridge determined on the basis of the signal outputted from the photosensor; and (d) in response to determination made in (c) that the types do not match, determining that the printing fluid cartridge in the mounted state is inappropriate. a cartridge-mounting portion in which a printing fluid cartridge is mountable, the printing fluid cartridge including a storage and an identification portion, the storage storing type information indicating a type of the printing fluid cartridge, the identification portion having a unique light transmission status differing depending on the type of the printing fluid cartridge; a photosensor disposed at the cartridge-mounting portion, the photosensor being configured to detect the unique light transmission status of the identification portion and output a signal differing depending on the detected unique light transmission status; and a controller configured to perform: (a) reading the type information from the storage of the printing fluid cartridge that is in a mounted state where the printing fluid cartridge is mounted in the cartridge-mounting portion, characterized in that the controller is further configured to perform: (b) determining the type of the printing fluid cartridge on the basis of both the read type information and the signal outputted from the photosensor (c) determining whether or not the type of the printing fluid cartridge determined on the basis of the read type information matches the type of the printing fluid cartridge determined on the basis of the signal outputted from the photosensor; and (d) in response to determination made in (c) that the types do not match, determining that the printing fluid cartridge in the mounted state is inappropriate. (a) reading the type information from the storage of the printing fluid cartridge that is in a mounted state where the printing fluid cartridge is mounted in the cartridge-mounting portion, characterized in that (b) determining the type of the printing fluid cartridge on the basis of both the read type information and the signal outputted from the photosensor (c) determining whether or not the type of the printing fluid cartridge determined on the basis of the read type information matches the type of the printing fluid cartridge determined on the basis of the signal outputted from the photosensor; and (d) in response to determination made in (c) that the types do not match, determining that the printing fluid cartridge in the mounted state is inappropriate.