A refrigerator comprising: a cabinet that defines a storage space; doors that are rotatably mounted on the cabinet by hinges to open/close the storage space; and an air purifier provided on an upper surface of the cabinet, the air purifier comprising: a case which is mounted on an upper surface of the cabinet and in which inlet holes and an outlet hole are formed; fan motor assemblies that are provided inside the case to force flow of air; filter assemblies that are mounted in the case to partition a space between the inlet holes and the fan motor assemblies and purify sucked air; a control unit configured to control driving of the fan motor assemblies; and a gas sensor that is connected to the control unit and configured to detect harmful gas in a kitchen space, wherein the control unit is configured to control driving of the fan motor assemblies through detection of the gas sensor, characterized in that upper ends of the doors extend to be identical to or higher than a height of the air purifier, such that the air purifier is shielded by the doors when the doors are in a closed position, wherein the case includes: an upper case having inclined surfaces on a front and both side circumferences, the inlet holes being formed in both side circumferences of the upper case and the outlet hole being formed in the front circumference of the upper case; a lower case coupled to the upper case; and a front discharge guide formed on a front inner side of the lower case and extending to a lower end of the outlet hole with a slope or round. a cabinet that defines a storage space; doors that are rotatably mounted on the cabinet by hinges to open/close the storage space; and an air purifier provided on an upper surface of the cabinet, the air purifier comprising: a case which is mounted on an upper surface of the cabinet and in which inlet holes and an outlet hole are formed; fan motor assemblies that are provided inside the case to force flow of air; filter assemblies that are mounted in the case to partition a space between the inlet holes and the fan motor assemblies and purify sucked air; a control unit configured to control driving of the fan motor assemblies; and a gas sensor that is connected to the control unit and configured to detect harmful gas in a kitchen space, a case which is mounted on an upper surface of the cabinet and in which inlet holes and an outlet hole are formed; fan motor assemblies that are provided inside the case to force flow of air; filter assemblies that are mounted in the case to partition a space between the inlet holes and the fan motor assemblies and purify sucked air; a control unit configured to control driving of the fan motor assemblies; and a gas sensor that is connected to the control unit and configured to detect harmful gas in a kitchen space, wherein the control unit is configured to control driving of the fan motor assemblies through detection of the gas sensor, characterized in that upper ends of the doors extend to be identical to or higher than a height of the air purifier, such that the air purifier is shielded by the doors when the doors are in a closed position, wherein the case includes: an upper case having inclined surfaces on a front and both side circumferences, the inlet holes being formed in both side circumferences of the upper case and the outlet hole being formed in the front circumference of the upper case; a lower case coupled to the upper case; and a front discharge guide formed on a front inner side of the lower case and extending to a lower end of the outlet hole with a slope or round. an upper case having inclined surfaces on a front and both side circumferences, the inlet holes being formed in both side circumferences of the upper case and the outlet hole being formed in the front circumference of the upper case; a lower case coupled to the upper case; and a front discharge guide formed on a front inner side of the lower case and extending to a lower end of the outlet hole with a slope or round.