A printing apparatus configured for printing on a front surface of a printing medium (WP), and thereafter printing on a back surface of the printing medium (WP), the apparatus comprising: a front surface print head configured for printing, on the front surface of the printing medium (WP) transported in a predetermined transport direction (X), cue marks indicating printing start positions in the transport direction (X) of front surface images, and printing the front surface images based on front surface image data with reference to the cue marks; and an elasticity information memory configured for storing elasticity information which is a degree of elasticity of the printing medium (WP) in the transport direction (X) after printing of the front surface images; a back surface image data corrector configured for creating corrected back surface image data, based on the elasticity information, by correcting image sizes of back surface image data to be formed on the back surface of the printing medium (WP); a detector configured for detecting the cue marks printed on the front surface of the printing medium (WP); a back surface print head for printing on the back surface of the printing medium (WP), back surface images based on the corrected back surface image data, with reference to the cue marks detected by the detector ; a page interval calculator configured for calculating a page interval in the transport direction (X) between the cue marks detected by the detector , before printing the back surface images based on the corrected back surface image data by the back surface print head ; characterized by a difference computing unit configured for calculating differences between the page interval and the image size in the transport direction (X) of the corrected back surface image data, when the corrected back surface image data is printed; and a setting unit configured for revising the elasticity information stored in the elasticity information memory based on the differences calculated by the difference computing unit . a front surface print head configured for printing, on the front surface of the printing medium (WP) transported in a predetermined transport direction (X), cue marks indicating printing start positions in the transport direction (X) of front surface images, and printing the front surface images based on front surface image data with reference to the cue marks; and an elasticity information memory configured for storing elasticity information which is a degree of elasticity of the printing medium (WP) in the transport direction (X) after printing of the front surface images; a back surface image data corrector configured for creating corrected back surface image data, based on the elasticity information, by correcting image sizes of back surface image data to be formed on the back surface of the printing medium (WP); a detector configured for detecting the cue marks printed on the front surface of the printing medium (WP); a back surface print head for printing on the back surface of the printing medium (WP), back surface images based on the corrected back surface image data, with reference to the cue marks detected by the detector ; a page interval calculator configured for calculating a page interval in the transport direction (X) between the cue marks detected by the detector , before printing the back surface images based on the corrected back surface image data by the back surface print head ; characterized by a difference computing unit configured for calculating differences between the page interval and the image size in the transport direction (X) of the corrected back surface image data, when the corrected back surface image data is printed; and a setting unit configured for revising the elasticity information stored in the elasticity information memory based on the differences calculated by the difference computing unit . <EOS>