A coupling with a safety valve function which connects tubes such as hoses or pipes to each other or connects the tube to another device, the coupling comprising: a coupling body (101, 172) including a mounting portion (103, 179) which is formed at one axial end of the coupling body (101, 172) and on which the tube or the other device is mounted, and a fluid passage (102, 187) which is formed inside the coupling body (101, 172); a coupling part (105, 180) including an attachment portion which is formed at one axial end of the coupling part (105, 180) and is attached to the coupling body (101, 172), and a coupling portion (110, 183) which is formed at the other axial end of the coupling part (105, 180) and is configured to be coupled with a counterpart coupling, and; a sealing member (133, 174) which is provided at the other axial end of the coupling body (101, 172) and is configured to close a gap with a sealing member of a counterpart coupling between the coupling and the counterpart coupling; characterized in that the coupling further comprises a deformation portion (135, 140, 190) which is formed in the coupling part (105, 180), which is configured to maintain a coupling condition with the counterpart coupling until a leak path is formed between the sealing member and the sealing member (133, 174) of the counterpart coupling when the deformation portion (135, 140, 190) is axially stretched by an axial tensile force which acts on the coupling part (105, 180) when pressure of a fluid within the coupling body (101, 172) unusually increases and the sealing member (133, 174) separates from the sealing member of the counterpart coupling to discharge the fluid to the outside. a coupling body (101, 172) including a mounting portion (103, 179) which is formed at one axial end of the coupling body (101, 172) and on which the tube or the other device is mounted, and a fluid passage (102, 187) which is formed inside the coupling body (101, 172); a coupling part (105, 180) including an attachment portion which is formed at one axial end of the coupling part (105, 180) and is attached to the coupling body (101, 172), and a coupling portion (110, 183) which is formed at the other axial end of the coupling part (105, 180) and is configured to be coupled with a counterpart coupling, and; a sealing member (133, 174) which is provided at the other axial end of the coupling body (101, 172) and is configured to close a gap with a sealing member of a counterpart coupling between the coupling and the counterpart coupling; characterized in that the coupling further comprises a deformation portion (135, 140, 190) which is formed in the coupling part (105, 180), which is configured to maintain a coupling condition with the counterpart coupling until a leak path is formed between the sealing member and the sealing member (133, 174) of the counterpart coupling when the deformation portion (135, 140, 190) is axially stretched by an axial tensile force which acts on the coupling part (105, 180) when pressure of a fluid within the coupling body (101, 172) unusually increases and the sealing member (133, 174) separates from the sealing member of the counterpart coupling to discharge the fluid to the outside.