Emission gas recycling equipment comprising: a passage for recycling a part of an emission gas from an exhaust side to an intake side of a combustion engine; and a control valve for controlling an amount of the part of the emission gas, which is recycled into the intake side through the passage, wherein the control valve includes: a housing having a pipe portion to provide a part of the passage; a butterfly valve accommodated in the pipe portion rotatable in a first direction and a second direction, wherein the first direction is defined as a rotational direction of the butterfly valve from a valve full open position to a valve full close position, and the second direction is opposite to the first direction, wherein the butterfly valve is rotatable in a range between the valve full open position and a predetermined position, to which the butterfly valve is rotatable by a predetermined degree from the valve full close position in the first direction; and valve open/close operation means (10-12, 14, 21-27, 31, 61, 62) adapted to operate the butterfly valve to open and to close equal to or more than one cycle across the valve full close position and thereafter to stop the butterfly valve at the valve full close position at the time when the engine stops or after the engine stops, characterized by a seal ring for sealing a clearance between an inner wall of the pipe portion and an outer wall of the butterfly valve in a case where the butterfly valve is positioned at the valve full close position, wherein the seal ring is accommodated in an outer diameter portion of the butterfly valve, wherein the seal ring is adapted to be elastically deformed in a radial direction of the pipe portion when the valve open/close operation means (10-12, 14, 21-27, 31, 61, 62) stops the butterfly valve at the valve full close position, so that an outer diameter surface of the seal ring is air-tightly attached to the inner wall of the pipe portion, and an outer diameter of the seal ring does not expand to be larger than an inner diameter of the pipe portion, wherein the seal ring has a C-shape with a clearance. a passage for recycling a part of an emission gas from an exhaust side to an intake side of a combustion engine; and a control valve for controlling an amount of the part of the emission gas, which is recycled into the intake side through the passage, wherein the control valve includes: a housing having a pipe portion to provide a part of the passage; a butterfly valve accommodated in the pipe portion rotatable in a first direction and a second direction, wherein the first direction is defined as a rotational direction of the butterfly valve from a valve full open position to a valve full close position, and the second direction is opposite to the first direction, wherein the butterfly valve is rotatable in a range between the valve full open position and a predetermined position, to which the butterfly valve is rotatable by a predetermined degree from the valve full close position in the first direction; and valve open/close operation means (10-12, 14, 21-27, 31, 61, 62) adapted to operate the butterfly valve to open and to close equal to or more than one cycle across the valve full close position and thereafter to stop the butterfly valve at the valve full close position at the time when the engine stops or after the engine stops, characterized by a housing having a pipe portion to provide a part of the passage; a butterfly valve accommodated in the pipe portion rotatable in a first direction and a second direction, wherein the first direction is defined as a rotational direction of the butterfly valve from a valve full open position to a valve full close position, and the second direction is opposite to the first direction, wherein the butterfly valve is rotatable in a range between the valve full open position and a predetermined position, to which the butterfly valve is rotatable by a predetermined degree from the valve full close position in the first direction; and valve open/close operation means (10-12, 14, 21-27, 31, 61, 62) adapted to operate the butterfly valve to open and to close equal to or more than one cycle across the valve full close position and thereafter to stop the butterfly valve at the valve full close position at the time when the engine stops or after the engine stops, characterized by a seal ring for sealing a clearance between an inner wall of the pipe portion and an outer wall of the butterfly valve in a case where the butterfly valve is positioned at the valve full close position, wherein the seal ring is accommodated in an outer diameter portion of the butterfly valve, wherein the seal ring is adapted to be elastically deformed in a radial direction of the pipe portion when the valve open/close operation means (10-12, 14, 21-27, 31, 61, 62) stops the butterfly valve at the valve full close position, so that an outer diameter surface of the seal ring is air-tightly attached to the inner wall of the pipe portion, and an outer diameter of the seal ring does not expand to be larger than an inner diameter of the pipe portion, wherein the seal ring has a C-shape with a clearance.