A radiation therapy apparatus has a multi-leaf collimator device, a driving gear, a torque wire and a driving unit. The multi-leaf collimator device has a pair of collimator components which respectively comprise a plurality of leaves arranged close to one another such that the leaves face one another across an irradiation axis, and configured to set a desired irradiation field by individually moving the leaves. The driving gear is engaged with a gear tooth of the each leaf, respectively. The torque wire is connected to a shaft center of the driving gear, respectively. The driving unit is configured to drive the driving gears through the torque wire.