A register error amount detection method comprising: the step of reading a captured image from an image capturing apparatus which captures an image of a region including a registration measurement mark printed in a margin of a printing product, the registration measurement mark including a first register mark group including a plurality of first register marks (P4 - P7) of different colors including a reference color and a second register mark group including a plurality of second register marks (P0 - P3) of the reference color, the plurality of second register marks (P0 - P3) being equal in number to the plurality of first register marks (P4 - P7), the plurality of first register marks (P4 - P7) being printed in a line at predetermined intervals in a first direction which is a vertical direction or horizontal direction of the printing product, and the plurality of second register marks (P0 - P3) being printed in a line at the predetermined intervals in the first direction at positions translated from the positions of the plurality of first register marks (P4 - P7) by a predetermined distance in a second direction perpendicular to the first direction; and the step of obtaining register error amounts between colors of patterns printed on the printing product based on positions of the plurality of first register marks (P4 - P7) and the plurality of second register marks (P0 - P3) in the read captured image, wherein the step of obtaining includes the step of obtaining register error amounts between colors in the first direction from distances between the first register mark of the reference color and the first register marks (P5 - P7) of remaining colors and distances between the second register mark at a position translated from a position of the first register mark of the reference color in the second direction and the second register marks (P1 - P3) at positions translated from positions of the first register marks (P5 - P7) of the remaining colors in the second direction, and the step of obtaining register error amounts between the colors in the second direction from a distance between the first register mark of the reference color and the second register mark at a position translated from the position of the first register mark of the reference color in the second direction and distances between the first register marks (P5 - P7) of the remaining colors and the second register marks (P1 - P3) at positions translated from the positions of the first register marks (P5 - P7) of the remaining colors in the second direction. the step of reading a captured image from an image capturing apparatus which captures an image of a region including a registration measurement mark printed in a margin of a printing product, the registration measurement mark including a first register mark group including a plurality of first register marks (P4 - P7) of different colors including a reference color and a second register mark group including a plurality of second register marks (P0 - P3) of the reference color, the plurality of second register marks (P0 - P3) being equal in number to the plurality of first register marks (P4 - P7), the plurality of first register marks (P4 - P7) being printed in a line at predetermined intervals in a first direction which is a vertical direction or horizontal direction of the printing product, and the plurality of second register marks (P0 - P3) being printed in a line at the predetermined intervals in the first direction at positions translated from the positions of the plurality of first register marks (P4 - P7) by a predetermined distance in a second direction perpendicular to the first direction; and the step of obtaining register error amounts between colors of patterns printed on the printing product based on positions of the plurality of first register marks (P4 - P7) and the plurality of second register marks (P0 - P3) in the read captured image, wherein the step of obtaining includes the step of obtaining register error amounts between colors in the first direction from distances between the first register mark of the reference color and the first register marks (P5 - P7) of remaining colors and distances between the second register mark at a position translated from a position of the first register mark of the reference color in the second direction and the second register marks (P1 - P3) at positions translated from positions of the first register marks (P5 - P7) of the remaining colors in the second direction, and the step of obtaining register error amounts between the colors in the second direction from a distance between the first register mark of the reference color and the second register mark at a position translated from the position of the first register mark of the reference color in the second direction and distances between the first register marks (P5 - P7) of the remaining colors and the second register marks (P1 - P3) at positions translated from the positions of the first register marks (P5 - P7) of the remaining colors in the second direction.