A deployable safety apparatus (100, 200) comprising: a sliding member (10, 110); a cylinder (14, 114) that accommodates the sliding member (10, 110) in an axially extending bore (13, 113) having an opening through which the sliding member (10, 110) increasingly protrudes from the bore (13, 113) during deployment; a push-up member (15, 115) including a cylindrical portion (19, 119) open at an end so as to be disposed before deployment to cover at least a part of the cylinder (14, 114) and a flange extending in a radially outward direction from the opening at the open end of the cylindrical portion (19, 119) or from an outer periphery of the cylindrical portion (19, 119), the push-up member (15, 115) during deployment being pushed up in one direction by the sliding member (10, 110); an ejected object (16, 116) that is pushed up during deployment while being supported by the flange of the push-up member (15, 115); and a power source (17, 117) that during deployment moves the sliding member (10, 110) in the cylinder (14, 114) to increasingly protrude from the bore (13, 113), wherein the sliding member (10, 110) has one end in the direction of increasing protrusion during deployment, and the cylindrical portion (19, 119) opposite its open end includes an end part, characterised in that the sliding member end has a cross-section of a non-circular shape and in that the end part of the cylindrical portion (19, 119) is provided with a first hole (53, 153) having an insertion opening (53a, 153a) into which the sliding member end is inserted from the cylinder, and at least a part of the length of the first hole (53, 153) is provided with a fitting portion to which the sliding member end is fitted, the fitting portion having a substantially identical cross-section to the cross-section of a non-circular shape of the sliding member end. a sliding member (10, 110); a cylinder (14, 114) that accommodates the sliding member (10, 110) in an axially extending bore (13, 113) having an opening through which the sliding member (10, 110) increasingly protrudes from the bore (13, 113) during deployment; a push-up member (15, 115) including a cylindrical portion (19, 119) open at an end so as to be disposed before deployment to cover at least a part of the cylinder (14, 114) and a flange extending in a radially outward direction from the opening at the open end of the cylindrical portion (19, 119) or from an outer periphery of the cylindrical portion (19, 119), the push-up member (15, 115) during deployment being pushed up in one direction by the sliding member (10, 110); an ejected object (16, 116) that is pushed up during deployment while being supported by the flange of the push-up member (15, 115); and a power source (17, 117) that during deployment moves the sliding member (10, 110) in the cylinder (14, 114) to increasingly protrude from the bore (13, 113), wherein the sliding member (10, 110) has one end in the direction of increasing protrusion during deployment, and the cylindrical portion (19, 119) opposite its open end includes an end part, characterised in that the sliding member end has a cross-section of a non-circular shape and in that the end part of the cylindrical portion (19, 119) is provided with a first hole (53, 153) having an insertion opening (53a, 153a) into which the sliding member end is inserted from the cylinder, and at least a part of the length of the first hole (53, 153) is provided with a fitting portion to which the sliding member end is fitted, the fitting portion having a substantially identical cross-section to the cross-section of a non-circular shape of the sliding member end.