A cartridge is set in a printer main unit, and has a remaining toner measurer
which
measures toner in a toner chamber upon setting of the cartridge. A cartridge memory
stores information of a remaining toner amount measured previously. CPU compares
the remaining toner amount measured newly with the remaining toner amount measured
previously and read from the cartridge memory. If there is an increase in the toner,
the cartridge is determined as improper cartridge reloaded with the toner. An alarm
signal is generated. Also, printing is inhibited. In another preferred embodiment,
shortage information is assigned to the cartridge upon using up the toner. The
cartridge, if it has the shortage information, is determined as improper. If a
characteristic of the toner is not within a reference range, the cartridge is determined
improper. In another preferred embodiment, an upper limit of the number of times
of toner reloading is predetermined. The cartridge is determined improper if the
reloading time number comes up to the upper limit. The improper cartridge is set
in a state in which operation is inhibited. Also, when the cartridge is disassembled,
the improper cartridge is inhibited from operating.
