Provided is a disk brake capable of improving fabrication efficiency. A transmission member (101) includes: an anti-rotation locking portion (130) formed on an outer circumferential portion of the transmission member, the anti-rotation locking portion being slidably fitted into a fitting area (72) on a cylinder (35) side so as to restrict rotation relative to the cylinder (35); and a seal groove (109) formed in an inserted portion (105), the seal groove storing a sealing member (118) for creating the cylinder (35) and a cam chamber (62). The anti-rotation locking portion (130) is fitted into the fitting area (72) on the cylinder (35) side before the sealing member (118) is positioned inside a hole (59) when the inserted portion (105) of the transmission member (101) is inserted into the hole (59).