An in-line strainer 1 includes: a cylindrical-shaped housing 2 having an inflow port 6 for liquid and an outflow port 7 which are coaxial with each other; and a strainer element 22 disposed in the housing 2. A cyclone cylindrical body 28 having a diametrically-reduced cylinder portion 30 whose inner diameter is reduced toward one end, and having a cyclone inflow port formed on the other end, is arranged inside the housing 2 such that the diametrically-reduced cylinder portion 30 is close to the inflow port 6, and that the cyclone inflow port is close to the outflow port 7. A cylindrical-shaped strainer element 22 having a closed first end and an open second end is in the cyclone cylindrical body 28, and an open second end 25 of the strainer element 22 is connected to the outflow port 7 of the housing 2.