An embodiment of this invention is directed to a leakage detection of a printhead. The embodiment executes leakage detection as follows in a printing apparatus which uses a reciprocally movable printhead. That is, the embodiment monitors a voltage appearing on a second power line which supplies, to the printhead, a second voltage that is used for detecting the current leakage from the printhead and is lower than a first voltage to be supplied to perform printing by the printhead through a first power line to which a capacitor is parallel-connected. If a timing at which detection of the current leakage is executed is detected, the embodiment performs control so as to execute detection of the current leakage based on the monitored voltage, by turning off supply of the first voltage and turning on supply of the second voltage.