A particle therapy system comprising: an irradiation control system configured to control a scanning path of the ion beam by controlling the scanning magnets (401, 402) based on a calculated scanning path, and a device for calculating said scanning path for particle irradiation, said device comprising: - an input device for inputting data relating to a target area movement; - an arithmetic device for performing arithmetic processing based on a result of data input of the input device and creating scanning path information for the target area; and - a display device for displaying the scanning path information; characterized in that the arithmetic device is adapted to calculate a scanning path by setting a pre-specified optional direction as a main direction for scanning irradiation positions with an ion beam using scanning magnets (401, 402), and the arithmetic device is adapted to set a plurality of straight lines parallel with the pre-specified direction and to arrange irradiation positions to be irradiated with an ion beam on the straight lines, wherein the pre-specified direction is set to be at moving direction of a target to be scanned, and the moving direction is determined to be the direction in which the movements of said target to be scanned have a greatest movement amplitude. an irradiation control system configured to control a scanning path of the ion beam by controlling the scanning magnets (401, 402) based on a calculated scanning path, and a device for calculating said scanning path for particle irradiation, said device comprising: - an input device for inputting data relating to a target area movement; - an arithmetic device for performing arithmetic processing based on a result of data input of the input device and creating scanning path information for the target area; and - a display device for displaying the scanning path information; characterized in that the arithmetic device is adapted to calculate a scanning path by setting a pre-specified optional direction as a main direction for scanning irradiation positions with an ion beam using scanning magnets (401, 402), and the arithmetic device is adapted to set a plurality of straight lines parallel with the pre-specified direction and to arrange irradiation positions to be irradiated with an ion beam on the straight lines, wherein the pre-specified direction is set to be at moving direction of a target to be scanned, and the moving direction is determined to be the direction in which the movements of said target to be scanned have a greatest movement amplitude. - an input device for inputting data relating to a target area movement; - an arithmetic device for performing arithmetic processing based on a result of data input of the input device and creating scanning path information for the target area; and - a display device for displaying the scanning path information; characterized in that the arithmetic device is adapted to calculate a scanning path by setting a pre-specified optional direction as a main direction for scanning irradiation positions with an ion beam using scanning magnets (401, 402), and the arithmetic device is adapted to set a plurality of straight lines parallel with the pre-specified direction and to arrange irradiation positions to be irradiated with an ion beam on the straight lines, wherein the pre-specified direction is set to be at moving direction of a target to be scanned, and the moving direction is determined to be the direction in which the movements of said target to be scanned have a greatest movement amplitude. the arithmetic device is adapted to calculate a scanning path by setting a pre-specified optional direction as a main direction for scanning irradiation positions with an ion beam using scanning magnets (401, 402), and the arithmetic device is adapted to set a plurality of straight lines parallel with the pre-specified direction and to arrange irradiation positions to be irradiated with an ion beam on the straight lines, wherein the pre-specified direction is set to be at moving direction of a target to be scanned, and the moving direction is determined to be the direction in which the movements of said target to be scanned have a greatest movement amplitude.