Multileaf collimator and radiation treatment device

A multileaf collimator for regulating a range irradiated with a radiation beam, comprising:

• a plurality of leaves arranged along a thickness direction, wherein
• each of the plurality of leaves comprising;
• a protruded portion protrudingly formed on a first side surface in a plate thickness direction of the leaf,
• a depressed portion formed in a second side surface in the plate thickness direction of the leaf, and configured to receive insertion of the protruded portion formed on another one of the plurality of leaves,
• a first curved surface formed between the first side surface of the leaf and a lateral surface of the protruded portion, and
• a second curved surface formed between the second side surface of the leaf and a lateral surface of the depressed portion.