To accurately predict number of sheets when number of printable sheets is calculated by calculating and displaying the number by considering a gradation level of each pixel of a memory picture, a temperature of a thermal head and using print media type in the case of converting a battery residue detected result into a printable number of sheets.

After an input picture signal is digitized and converted into gradation level data, the signal is stored in a picture memory 2. A thermistor 9 detects a temperature of a thermal head 5. A media detector detects media deciding markers attached to an ink, sheets of print media, an ink cartridge or the like containing the ink, sends the marks to a system controller 3, which decides print conditions of a thermal head temperature, type of the media, a printing speed or the like. The controller 3 detects a residual capacity of a battery 10 from a battery voltage value, converts it to number of printable sheets, and displays the result on a residue display unit 11.