An image forming system comprising: a first image forming portion that forms an image on an outer circumferential surface of a can body rotating in a circumferential direction; characterized in that the image forming system further comprises a first obtaining unit that obtains information related to rotation angle of the can body when image formation by the first image forming portion is started; a second image forming portion that forms an image on the can body rotating in the circumferential direction after the image is formed on the can body by the first image forming portion; a second obtaining unit that obtains information related to rotation angle of the can body when image formation by the second image forming portion is started; a data storing portion that stores image data of the image formed by the second image forming portion; and a determination unit that determines a starting position of reading based on an angle difference, which is a difference between a rotation angle specified by the information related to the rotation angle obtained by the first obtaining unit and a rotation angle specified by the information related to the rotation angle obtained by the second obtaining unit, wherein the determination unit supplies the read image data to the second image forming portion and the second image forming portion forms an image on the outer circumferential surface of the can body rotating in the circumferential direction, and wherein the first image forming portion and the second image forming portion are designed to form an image on the outer circumferential surface of the can body by ejecting ink from above the can body in a lying state. a first image forming portion that forms an image on an outer circumferential surface of a can body rotating in a circumferential direction; characterized in that the image forming system further comprises a first obtaining unit that obtains information related to rotation angle of the can body when image formation by the first image forming portion is started; a second image forming portion that forms an image on the can body rotating in the circumferential direction after the image is formed on the can body by the first image forming portion; a second obtaining unit that obtains information related to rotation angle of the can body when image formation by the second image forming portion is started; a data storing portion that stores image data of the image formed by the second image forming portion; and a determination unit that determines a starting position of reading based on an angle difference, which is a difference between a rotation angle specified by the information related to the rotation angle obtained by the first obtaining unit and a rotation angle specified by the information related to the rotation angle obtained by the second obtaining unit, wherein the determination unit supplies the read image data to the second image forming portion and the second image forming portion forms an image on the outer circumferential surface of the can body rotating in the circumferential direction, and wherein the first image forming portion and the second image forming portion are designed to form an image on the outer circumferential surface of the can body by ejecting ink from above the can body in a lying state.