The multi-leaf collimator (60) comprises a plurality of leaves (70) arranged in the thickness direction, a driving device (90) for moving the leaves (70) forward and backward with respect to the radiation (Sr) And a recognition mark (102) recognizable at least from a direction perpendicular to both the advancing / retreating direction of the leaf (70) and the thickness direction of the leaf (70), and a plurality of leaves (70 ) Of the recognition marks (102) adjacent to each other in the thickness direction than the gap (d 1) between the leaves (70) adjacent in the thickness direction in a state where the recognition marks (102) are arranged at the preset reference position The gap (d 2) was made large.このマルチリーフコリメータ(60)は、厚さ方向に並べられた複数枚のリーフ(70)と、放射線(Sr)に対してリーフ(70)を進退させる駆動装置(90)と、リーフ(70)の位置を検出するため、リーフ(70)の進退方向とリーフ(70)の厚さ方向との両方に垂直な方向から少なくとも認識可能な認識マーク(102)と、を備え、複数のリーフ(70)が予め設定された基準位置(P)に配された状態で、厚さ方向で隣り合うリーフ(70)同士の隙間(d1)よりも、厚さ方向で隣り合う認識マーク(102)同士の隙間(d2)が大きくなるようにした。
