A reading time setting section (44) determines a read area for an imaging section (25) on the basis of color chart positional data (id). The imaging section (25) reads an image on printing paper during the reading time and readout image data (rd) is stored in an image data storage section (45). A reference mark detecting section (46) detects the positions of reference marks from the readout image data (rd). A color chart actual position calculation section (47) corrects a tilt of a color chart determined from the positions of the reference marks and calculates an actual position of each of color chart fields (cr). An image data readout section (48) reads out image data on a color chart field corresponding to the calculated actual position. At the same time, image data on a white color field immediately above the color chart field is also read out. A white color correction section (49) produces a white reference on the basis of the image data on the white color field and corrects the image data on the color chart field. A color chart information determination section (50) measures color chart information, such as a color density and a dot percentage, about each of the color chart fields. This printing press determines a reading time on the basis of the position of the color chart at the time of printing plate recording and thereby allows imaging of an area including the color chart on the printing paper being transported.