To provide a sealing device for brake hydraulic operating means for preventing falling off of cap while maintaining stable sealing performance (sealing capacity) and easily taking off the cap at a time of connecting hydraulic pipe.

A flow passage 10e communicating to a hydraulic chamber is formed at a connection port 10b. An end part of a body part 30b of the cap 30 gets close to a mouth part of the flow passage 10e to cut off communication of the connection port 10b and the flow passage 10e. And a surface of a dimple 30c of a head part 30a standing in a row from the body part 30b elastically deforms in a radial direction outside and gets close to an opening end surface of the connection port 10b (forming a double seal part). Inside of the connection port 10b is kept in a vacuum status and the head part 30 is sucked on the opening end surface.