A reel unit (2, 302) for a spinning reel (100, 300), the spinning reel (100, 300) being attachable to a fishing rod, the spinning reel configured to forwardly release a fishing line from a front side of the spinning reel (100, 300), the reel unit (2, 302) comprising: a chassis (2a, 302a) including a mechanism attachment space at a lateral side thereof, a first opening (30, 330) extending through a front edge of the chassis (2a, 302a), and a second opening (31, 331) extending through a rear edge of the chassis (2a, 302a), the second opening (31, 331) disposed on an opposite side of the first opening (30, 330); a lid member detachably attached to the chassis (2a, 302a) to close the mechanism attachment space; a guard member (26, 326) including a boss (26a, 326a) being inserted into the second opening (31, 331) from the rear edge of the chassis (2a, 302a), the guard member (26, 326) being attached to the chassis (2a, 302a) and the lid member from behind to cover the chassis (2a, 302a) and the lid member; a tubular part (25, 325) being disposed between the first opening (30, 330) and the second opening (31, 331) within the mechanism attachment space and arranged to be liquid-tight; and a screw member (27, 327) passing through the first opening (30, 330) and being screwed into the boss (26a, 326a), the screw member (27, 327) having a head (27a, 327a) being held inside the tubular part (25, 325), wherein the first opening (30, 330) and the second opening (31, 331) continue to the mechanism attachment space, at least a part of the tubular part (25, 325) is disposed between the first opening (30, 330) and the second opening (31, 331) within the mechanism attachment space characterized in that the reel unit (2, 302) further includes a first seal member (28, 328) being configured to seal a clearance between the tubular part (25, 325) and the first opening (30, 330), and a second seal member (29, 329) being configured to seal a clearance between the tubular part (25, 325) and the second opening (31, 331). a chassis (2a, 302a) including a mechanism attachment space at a lateral side thereof, a first opening (30, 330) extending through a front edge of the chassis (2a, 302a), and a second opening (31, 331) extending through a rear edge of the chassis (2a, 302a), the second opening (31, 331) disposed on an opposite side of the first opening (30, 330); a lid member detachably attached to the chassis (2a, 302a) to close the mechanism attachment space; a guard member (26, 326) including a boss (26a, 326a) being inserted into the second opening (31, 331) from the rear edge of the chassis (2a, 302a), the guard member (26, 326) being attached to the chassis (2a, 302a) and the lid member from behind to cover the chassis (2a, 302a) and the lid member; a tubular part (25, 325) being disposed between the first opening (30, 330) and the second opening (31, 331) within the mechanism attachment space and arranged to be liquid-tight; and a screw member (27, 327) passing through the first opening (30, 330) and being screwed into the boss (26a, 326a), the screw member (27, 327) having a head (27a, 327a) being held inside the tubular part (25, 325), wherein the first opening (30, 330) and the second opening (31, 331) continue to the mechanism attachment space, at least a part of the tubular part (25, 325) is disposed between the first opening (30, 330) and the second opening (31, 331) within the mechanism attachment space characterized in that the reel unit (2, 302) further includes a first seal member (28, 328) being configured to seal a clearance between the tubular part (25, 325) and the first opening (30, 330), and a second seal member (29, 329) being configured to seal a clearance between the tubular part (25, 325) and the second opening (31, 331). a first seal member (28, 328) being configured to seal a clearance between the tubular part (25, 325) and the first opening (30, 330), and a second seal member (29, 329) being configured to seal a clearance between the tubular part (25, 325) and the second opening (31, 331).