A connector, comprising: a housing including a terminal mounting portion that is suitable for being at least partly fitted into a shaft hole formed in a wall surface of a mounting member, a receptacle into which a mating connector can be at least partly fitted, and a mounting flange provided between the terminal mounting portion and the receptacle is suitable for being mounted on the wall surface of the mounting member; a terminal mounted into the terminal mounting portion such that a portion thereof at least partly projects into the receptacle, and a seal ring mounted on the mounting flange facing the mounting member for sealing between the mounting flange and the wall surface of the mounting member, wherein: the seal ring includes a ring main body surrounding the outer periphery of the terminal mounting portion and fixing portions for fixing the ring main body to the mounting flange, the ring main body being annular and having a rectangular shape, each fixing portion includes at least one bulging portion and at least one locking portion projecting from the bulging portion toward a side opposite to a sealing surface toward the mounting member and engageable with at least one locking hole formed in the housing, characterised in that the fixing portions are formed at or near an inner peripheral side and at each of four corners of the ring main body. a housing including a terminal mounting portion that is suitable for being at least partly fitted into a shaft hole formed in a wall surface of a mounting member, a receptacle into which a mating connector can be at least partly fitted, and a mounting flange provided between the terminal mounting portion and the receptacle is suitable for being mounted on the wall surface of the mounting member; a terminal mounted into the terminal mounting portion such that a portion thereof at least partly projects into the receptacle, and a seal ring mounted on the mounting flange facing the mounting member for sealing between the mounting flange and the wall surface of the mounting member, wherein: the seal ring includes a ring main body surrounding the outer periphery of the terminal mounting portion and fixing portions for fixing the ring main body to the mounting flange, the ring main body being annular and having a rectangular shape, each fixing portion includes at least one bulging portion and at least one locking portion projecting from the bulging portion toward a side opposite to a sealing surface toward the mounting member and engageable with at least one locking hole formed in the housing, characterised in that the fixing portions are formed at or near an inner peripheral side and at each of four corners of the ring main body. the seal ring includes a ring main body surrounding the outer periphery of the terminal mounting portion and fixing portions for fixing the ring main body to the mounting flange, the ring main body being annular and having a rectangular shape, each fixing portion includes at least one bulging portion and at least one locking portion projecting from the bulging portion toward a side opposite to a sealing surface toward the mounting member and engageable with at least one locking hole formed in the housing, characterised in that the fixing portions are formed at or near an inner peripheral side and at each of four corners of the ring main body.