A compact strainer having a small pressure loss which is easily cleaned without inserting and detaching screens in and from a strainer casing. Front and rear end portions of a tubular casing are respectively provided with an inlet and an outlet. A barrier divides in two a linear channel between the inlet and the outlet along a flowing direction and is provided on the outlet side so as to face the inlet. A filter portion surrounding the inlet is constituted by the barrier, a pair of screens laterally opposing each other and arranged at a predetermined interval are provided, and the upper and lower portions of an inner surface of an outer wall of the casing, and upper and lower regions of the outer wall are provided with opening portions with lids which make the inside of the filter portion communicate with the outside.