Printing apparatus

A printing apparatus comprising:

• a printing unit that forms an image on a target printing surface of a printing medium by relatively moving with respect to the printing medium;
• an elastic wave radiation unit that radiates elastic waves, which are pulses or burst waves in which a radiation direction is defined, toward the target printing surface;
• a reception unit that receives the elastic waves that are radiated from the elastic wave radiation unit and reflected by the target printing surface;
• and
• a control unit which measures the time of arrival taken for elastic waves that are radiated from the elastic wave radiation unit to arrive at the reception unit, and stops relative movement when the time of arrival is shorter than a defined time,
• wherein the defined time is a time of arrival in which a distance that is obtained by adding a difference in the distance from the printing unit to the printing medium and the distance from the elastic wave radiation unit to the printing medium to an allowable minimum distance between the printing unit and the printing medium that is established in advance, is equivalent to a distance from the elastic wave radiation unit to the printing medium.