A connector comprising: a terminal fitting; a housing accommodating the terminal fitting therein and including a fitting portion adapted to be inserted and fitted into a mating fitting portion along a connector insertion direction, and adapted to be electrically connected to a mating terminal fitting of a mating apparatus; a water stop member including an annular water stop main body, an inner circumferential surface of which is coaxially in close contact with an outer circumferential wall surface of the fitting portion, the water stop member being elastically deformable so as to fill an annular gap between the fitting portion and the mating fitting portion by the water stop main body at a fitting completion position of the fitting portion and the mating fitting portion; and a rotation stop structure provided at a position between the housing and the water stop member to restrict relative rotation in a circumferential direction of the water stop member relative to the fitting portion, wherein the rotation stop structure includes a portion to be accommodated protruding from an annular end surface (71d,71e) in an axial direction of the water stop main body, and an accommodating portion provided in the housing to maintain the water stop member at an attachment completion position to the fitting portion by inserting from an opening and accommodating the portion to be accommodated, the connector being characterised by that: the portion to be accommodated is formed in a piece body shape having a locked end at a first end and a locked end at a second end in the circumferential direction, and a first locked wall surface on the inner circumferential surface side and a second locked wall surface on an outer circumferential surface side of the water stop main body, the first locked wall surface and the second locked wall surface extending along the circumferential direction and the axial direction, and the accommodating portion has a locking wall at a first end in the circumferential direction capable of locking the locked end at the first end, a locking wall at a second end in the circumferential direction capable of locking the locked end at the second end, a first locking wall surface capable of locking the first locked wall surface, and a second locking wall surface capable of locking the second locked wall surface. a terminal fitting; a housing accommodating the terminal fitting therein and including a fitting portion adapted to be inserted and fitted into a mating fitting portion along a connector insertion direction, and adapted to be electrically connected to a mating terminal fitting of a mating apparatus; a water stop member including an annular water stop main body, an inner circumferential surface of which is coaxially in close contact with an outer circumferential wall surface of the fitting portion, the water stop member being elastically deformable so as to fill an annular gap between the fitting portion and the mating fitting portion by the water stop main body at a fitting completion position of the fitting portion and the mating fitting portion; and a rotation stop structure provided at a position between the housing and the water stop member to restrict relative rotation in a circumferential direction of the water stop member relative to the fitting portion, wherein the rotation stop structure includes a portion to be accommodated protruding from an annular end surface (71d,71e) in an axial direction of the water stop main body, and an accommodating portion provided in the housing to maintain the water stop member at an attachment completion position to the fitting portion by inserting from an opening and accommodating the portion to be accommodated, the connector being characterised by that: the portion to be accommodated is formed in a piece body shape having a locked end at a first end and a locked end at a second end in the circumferential direction, and a first locked wall surface on the inner circumferential surface side and a second locked wall surface on an outer circumferential surface side of the water stop main body, the first locked wall surface and the second locked wall surface extending along the circumferential direction and the axial direction, and the accommodating portion has a locking wall at a first end in the circumferential direction capable of locking the locked end at the first end, a locking wall at a second end in the circumferential direction capable of locking the locked end at the second end, a first locking wall surface capable of locking the first locked wall surface, and a second locking wall surface capable of locking the second locked wall surface. the portion to be accommodated is formed in a piece body shape having a locked end at a first end and a locked end at a second end in the circumferential direction, and a first locked wall surface on the inner circumferential surface side and a second locked wall surface on an outer circumferential surface side of the water stop main body, the first locked wall surface and the second locked wall surface extending along the circumferential direction and the axial direction, and the accommodating portion has a locking wall at a first end in the circumferential direction capable of locking the locked end at the first end, a locking wall at a second end in the circumferential direction capable of locking the locked end at the second end, a first locking wall surface capable of locking the first locked wall surface, and a second locking wall surface capable of locking the second locked wall surface.