To provide a vacuum breaking valve that can change from forcible valve closing to forcible valve opening and vice versa, opening/closing pressure.

A valve casing comprising a body 1 and a plug 2 is configured to form an inlet port 5 connected to a fluid piping system, an atmosphere port 4 opened to the atmosphere, and a valve chamber 3 communicating with the inlet port 5 and the atmosphere port 4. An annular valve seat 7 is provided between the atmosphere port 4 and the valve chamber 3. A valve body 8 to open/close the annular valve seat 7 is arranged in the valve chamber 3. A spring 9 to bias the valve body 8 to the annular valve seat 7 is arranged between the valve body 8 and the plug 2. The plug 2 is screw-connected to the body 1 to be advanceably/retractably operable from the outside. One end of the spring 9 is press-fitted to the valve body 8 while the other end of the spring 9 is press-fitted to the plug 2. If the plug 2 is screwed in, it allows valve opening while the inlet port 5 is in a higher vacuum state. If the plug 2 is further screwed in, it allows forcible valve closing. In an opposite manner, if the plug 2 is loosened, it allows valve opening while the inlet port 5 is in a lower vacuum state. If the plug 2 is further loosened, it allows forcible valve opening.