PURPOSE: To provide an ink residual amount detector capable of detecting the residual amount of ink even when an ink holding material is provided in an ink tank regardless of the shape of the ink tank without generating the electrolysis of ink.

CONSTITUTION: In a thermal ink jet printer, a temp. detection means 1 is provided in a heater wafer 2 or in the vicinity of the heater wafer 2. The temp. rise of the heater water 2 or in the vicinity thereof at the time of the injection of an ink drop is related to the residual amount of ink. Temp. data before the start of injection and temp. data at the time of the completion of the injection of a predetermined number of ink drops are taken in and the residual amount can be detected from the difference between both data.