A cover for preventing misoperation is easily and certainly attached/detached to/from an operating piece for manual operation provided for a fluid pressure control device. It is attached so as not to be lost even when the cover is detached for manual operation. For this purpose, retaining grooves 7a and 7b are formed on the outer face of a plunger-type operating piece 3 provided on the top face of the body 4 so as to be projected. A cylindrical cover 5 is provided with a hook 10 which is resiliently retained by the retaining groove 7a or 7b and a string-shaped connecting member 12 which is connected to the operating piece 3, thereby preventing the cover 5 from being lost. The height of the cover 5 is set to be equal to or higher than that of the operating piece 3 in a non-operating position.