A hydraulic actuator comprising: an actuator main portion formed by a tube having a cylindrical shape which is expanded and contracted by pressure of fluid, and a sleeve formed as a structural body in which cords oriented in a predetermined direction are braided, the sleeve being configured to cover an outer periphery of the tube; and a sealing mechanism (200, 200A, 200B, 200C) which seals an end portion of the actuator main portion in an axial direction, wherein: the sealing mechanism (200, 200A, 200B, 200C) comprises: a sealing member (210, 210A, 210B, 210C) having a body portion (211, 211A, 211B, 211C) and a flange portion (212, 212A); a caulking member (230, 230A, 230B, 230C) which caulks the actuator main portion in conjunction with the sealing member (210, 210A, 210B, 210C); and a first locking element which locks the sleeve; the body portion (211, 211A, 211B, 211C) inserted into the tube; the flange portion (212, 212A) is continued to the body portion (211, 211A, 211B, 211C) and an outer diameter of the flange portion (212, 212A) along a radial direction of the actuator main portion is larger than an outer diameter of the body portion (211, 211A, 211B, 211C); the first locking element locks the sleeve at an outer side of the body portion (211, 211A, 211B, 211C) in the radial direction; characterised in that the first locking element is a first locking ring and the sleeve comprises a first folded portion folded via the first locking ring; and the caulking member (230, 230A, 230B, 230C) caulks the tube into which the body portion (211, 211A, 211B, 211C) is inserted, the sleeve located at the outer side of the tube in the radial direction, and the first folded portion in conjunction with the sealing member (210, 210A, 210B, 210C). an actuator main portion formed by a tube having a cylindrical shape which is expanded and contracted by pressure of fluid, and a sleeve formed as a structural body in which cords oriented in a predetermined direction are braided, the sleeve being configured to cover an outer periphery of the tube; and a sealing mechanism (200, 200A, 200B, 200C) which seals an end portion of the actuator main portion in an axial direction, wherein: the sealing mechanism (200, 200A, 200B, 200C) comprises: a sealing member (210, 210A, 210B, 210C) having a body portion (211, 211A, 211B, 211C) and a flange portion (212, 212A); a caulking member (230, 230A, 230B, 230C) which caulks the actuator main portion in conjunction with the sealing member (210, 210A, 210B, 210C); and a first locking element which locks the sleeve; a sealing member (210, 210A, 210B, 210C) having a body portion (211, 211A, 211B, 211C) and a flange portion (212, 212A); a caulking member (230, 230A, 230B, 230C) which caulks the actuator main portion in conjunction with the sealing member (210, 210A, 210B, 210C); and a first locking element which locks the sleeve; the body portion (211, 211A, 211B, 211C) inserted into the tube; the flange portion (212, 212A) is continued to the body portion (211, 211A, 211B, 211C) and an outer diameter of the flange portion (212, 212A) along a radial direction of the actuator main portion is larger than an outer diameter of the body portion (211, 211A, 211B, 211C); the first locking element locks the sleeve at an outer side of the body portion (211, 211A, 211B, 211C) in the radial direction; the sleeve comprises a first folded portion folded via the first locking ring; and the caulking member (230, 230A, 230B, 230C) caulks the tube into which the body portion (211, 211A, 211B, 211C) is inserted, the sleeve located at the outer side of the tube in the radial direction, and the first folded portion in conjunction with the sealing member (210, 210A, 210B, 210C).