A wet-type image forming apparatus and method is provided to sense and
maintain a toner concentration level of a developer, and includes a
counter for counting the number of dots of input print data, a memory for
storing an average coverage of a print medium which corresponds to a
predetermined dot number of the print data and storing a lookup table for
consumption quantities of carrier and toner which correspond to the
average coverage, and a control unit for calculating a toner
concentration of a developer that remains in a developer supplying unit
by recognizing consumption quantities of the carrier and the toner that
are stored in the memory based on the counted dot number.