To simplify the attachment and detachment of transparent covers having excellent weather resistance without lowering its transparency, by connecting and disconnecting two axially divided cylindrical transparent covers to/from each other by attaching/detaching means.

Two divided transparent covers 11, 12 are formed by axially dividing a cylindrical transparent cover 10 into two. A plurality of attaching/ detaching means 13, for example, catch clamps are mounted in the axial direction of the front/rear surfaces of two divided transparent covers 11, 12. The catch clamps 13 are attached on the surfaces of the transparent covers 11, 12 by holes opened through two divided transparent covers 11, 12, mounting plates 13A, 13B and screws. Two divided transparent covers 11, 12 can be easily connected/disconnected to/ from each other by the operation of the catch clamps 13. Therefore, the cylindrical transparent cover 10 can be easily attached/detached to/from a valve. Also, the transparent cover 10 can be easily cleaned and oil leakage can be easily confirmed.