A controller (10) for controlling a process nozzle (20) and a laser oscillator (22) includes: an analyzer (12); a calculator (13) for calculating angle of a virtual corner part formed by two main process paths; a determining unit (14) for determining whether distance between the two main process paths corresponding to the circular-arc process path(s) is smaller than a first predetermined value, and determining whether the calculated angle is smaller than a second predetermined value; and a changing unit (15) for changing a laser process condition in the circular-arc process path(s) from a laser process condition in the main process paths when it is determined that the linear distance is smaller than the first predetermined value and the angle is smaller than the second predetermined value.