Being driven by the motor where the long leaf where the multi-blade collimator for the radiotherapy device lines up, phase separating in cross direction, it has one array at least, each leaf through drive expedient, is connected to the leaf and is related, the leaf in that longitudinal direction to expand or contract, or, as for drive expedient to have the sub frame where the motor you can install one part at least, the sub frame to be installed in the position where in the direction which it crosses vis-a-vis cross direction and longitudinal direction it is segregated from the aforementioned leaf array, to have the plural feed screws which distribution facilities are done for longitudinal direction, each screw to be driven by the motor, in addition operation to the leafIn order to be possible, being connected, it drives that leaf. Because of this, spatial efficiency increases, it is possible to designate the drive system as module system. As for the plural motors which are installed on the sub frame, it can install in the first longitudinal direction end, remainder of the motor which is installed on the sub frame is installed in the longitudinal direction end where second opposes. As for these feed screws which are not in the edge of array, desirably, with the second feed screw which is driven by the motor which is installed in one feed screw which is driven by the motor which is installed in the same longitudinal direction end and the longitudinal direction end which opposes it adjoins on each side section. As a result, the motor is arranged in the gap, and opposite can provide the space in order to install the motor between that gap. As for opposite of the motor, in order to be able to obtain necessary clearance, repeating to the top and bottom, it is possible to arrange, but as for this, as for the feed screw where from the leaf at one among two intervals you can install the feed screw inside the sub frame, adjoin to cross direction the fact that it is installed
