A printing apparatus which prints a print image onto a printing medium based on image data, includes a plurality of nozzles which discharge ink onto the printing medium based on the image data while relatively moving with respect to the printing medium, an intensity detector which irradiates the printing medium with irradiation light to detect a light intensity for detection which is an intensity of light through the printing medium based on the irradiation light, and a defective nozzle detector which detects a bias of a distribution of dots with the ink formed on the printing medium based on the light intensity for detection to judge whether a defective nozzle is caused based on the bias of the distribution of the dots.