Various fluids such as water, oil, gas, air, and steam flowing through various piping lines contain foreign matter in the fluid, corrosion in the piping, gaskets, and other debris from separation. If the fluid is left as it is, the valve seats of various valves installed in the piping lines may be damaged, resulting in shortened service life, and the various devices may not be operated properly or the devices may be damaged. To prevent these problems, strainers that separate and remove foreign matter and dirt from fluids play an important role in the piping line. This strainer has a built-in screen that filters foreign matter and dust in the fluid, and has a structure that allows foreign matter and dust accumulated in the screen to be removed and cleaned while the strainer body remains connected to the piping.