To provide a strainer device for use in a deep vacuum draining-compaction draining method for lowering a groundwater level.

The strainer device is formed of a long casing pipe (1) and a sheath pipe (2) sheathing the same. The casing pipe (1) is formed by welding a plurality of inner pipe bodies which are divided sections of the entire pipe and have different lengths, together in one body. Then, an inner pipe body (11) located at a lowermost stage has a closed-end sand stop portion (1') arranged thereon, and a plurality of water absorbing holes (3) bored in an outer peripheral surface thereof at locations immediately above the sand stop portion. Each water absorbing hole is a combination of a slit (31) and a triangular hole (32). Further, an annular bearing seat (6) is arranged on an outer peripheral surface of the sand stop portion (1'). The sheath pipe (2) is formed by welding divided sheath pipe bodies (21), (22), ... (2n) which are divided corresponding to the length (L) of the inner pipe (1), together in one body. The sheath pipe (2) has a plurality of spacers (5) arranged on an inner peripheral surface thereof to secure a predetermined clearance (S) between the inner pipe body and the sheath pipe body. The sheath pipe (2) has a water passage port (4) such as a window, and a slit in an outer peripheral surface thereof, and a water passable hole shielding body (7) mounted on the outer peripheral surface.