An outdoor unit of an air conditioner, comprising: a casing having a generally rectangular parallelepiped box shape; a partition plate extending vertically so as to divide the inside of the casing; a shut-off valve support member having a plate shape, configured to support a gas side shut-off valve and a liquid side shut-off valve to which a refrigerant pipe on an indoor unit side is connected, and arranged to be extended across a first fixing portion and a second fixing portion of an outdoor unit, the shut-off valve support member comprising: an attachment portion, an interference prevention portion located at a position opposite to the attachment portion when viewed in the longitudinal direction, away from the service port in a thickness direction of the shut-off valve support member, the interference prevention portion being disposed so as to overlap with the service port when viewed in the thickness direction; and a stepped portion formed between the attachment portion and the interference prevention portion, characterized in that the shut-off valve (61, 62) is attached to the attachment portion, with a service port (61a, 62a) of the gas side shut-off valve and the liquid side shut-off valve side by side along a longitudinal direction of the shut-off valve support member protruding in a direction perpendicular to the longitudinal direction of the shut-off valve support member, indoor side connection ports (61b, 62b) of the shut-off valves (61, 62) protruding in the opposite direction from the protruding direction of the service port (61a, 62a), the service port being used for at least one of filling refrigerant and drawing vacuum, the shut-off valve support member being configured to be extended between a first fixing portion formed on the partition plate or on a surface of the casing near the partition plate and a second fixing portion formed on a surface of the casing, the surface facing the partition plate; and the outdoor unit further comprising the shut-off valve (61, 62) which is supported by the shut-off valve support member and to which a refrigerant pipe on an indoor unit side is connected. a casing having a generally rectangular parallelepiped box shape; a partition plate extending vertically so as to divide the inside of the casing; a shut-off valve support member having a plate shape, configured to support a gas side shut-off valve and a liquid side shut-off valve to which a refrigerant pipe on an indoor unit side is connected, and arranged to be extended across a first fixing portion and a second fixing portion of an outdoor unit, the shut-off valve support member comprising: an attachment portion, an interference prevention portion located at a position opposite to the attachment portion when viewed in the longitudinal direction, away from the service port in a thickness direction of the shut-off valve support member, the interference prevention portion being disposed so as to overlap with the service port when viewed in the thickness direction; and a stepped portion formed between the attachment portion and the interference prevention portion, characterized in that the shut-off valve (61, 62) is attached to the attachment portion, with a service port (61a, 62a) of the gas side shut-off valve and the liquid side shut-off valve side by side along a longitudinal direction of the shut-off valve support member protruding in a direction perpendicular to the longitudinal direction of the shut-off valve support member, indoor side connection ports (61b, 62b) of the shut-off valves (61, 62) protruding in the opposite direction from the protruding direction of the service port (61a, 62a), the service port being used for at least one of filling refrigerant and drawing vacuum, the shut-off valve support member being configured to be extended between a first fixing portion formed on the partition plate or on a surface of the casing near the partition plate and a second fixing portion formed on a surface of the casing, the surface facing the partition plate; and the outdoor unit further comprising the shut-off valve (61, 62) which is supported by the shut-off valve support member and to which a refrigerant pipe on an indoor unit side is connected.