The present invention provides an ink jet printing apparatus of a low-cost and simple construction which can detect with high reliability a gap between a print medium and a print head mounted on a carriage. The ink jet printing apparatus, which reciprocally moves in a predetermined scan direction the carriage holding the print head for ejecting ink onto the print medium, includes a gap changing mechanism for changing the gap between the print head held in the carriage and the print medium and a control unit for controlling a driving of the gap changing mechanism and a reciprocal movement of the carriage, wherein the control unit drives the gap changing mechanism and reciprocally moves the carriage to check the operation state of the gap changing mechanism.