Particle beam irradiation system and particle beam irradiation method

A particle irradiation system for repeating an operation of moving an incident particle beam along a first axis and for making the incident particle beam dwell so as to irradiate the particle beam onto a target, comprising:

• a first deflector having a maximum deflection amount which enables the first deflector to move the particle beam along the first axis to a maximum width of the target;
• a second deflector having a maximum deflection amount which enables the second deflector to move the particle beam along the first axis, the maximum deflection amount by the second deflector being less than the maximum deflection amount by the first deflector;
• and
• a scanning control apparatus which controls the first deflector and the second deflector,
• wherein the scanning control apparatus is configured to (i) perform a control in which the particle beam is moved by increasing at least a deflection amount by the second deflector when the particle beam is moved, and (ii) subsequently perform a deflection substitution control in which a deflection by the second deflector is substituted by a deflection by the first deflector by decreasing the deflection amount by the second deflector and changing a deflection amount by the first deflector so as to make a position of the particle beam in the target dwell.