The invention is intended to shorten a positioning time required for
forming an irradiation area with high accuracy using a number of leaf
plates, and to reduce physical and mental burdens imposed on patients. A
multi-leaf collimator comprises leaf plate driving body each including a
plurality of movable leaf plates and provided respectively on one side and
the other side, the plurality of leaf plates of the leaf plate driver on
one side and the plurality of leaf plates of the leaf plate driver on the
other side being disposed in an opposing relation to form an irradiation
field of a radiation beam between the opposing leaf plates. Each of the
leaf plate driving body includes a motor provided in common to the
plurality of leaf plates. Driving force of the motor can be transmitted to
the plurality of leaf plates at the same time through a pinion gear, upper
and lower air cylinders, and upper and lower guides. Also, the driving
force can be cut off selectively for each leaf plate.
