A degasifier is provided in which the deterioration in sealing property (deterioration in airtightness) is prevented while sealing members to be placed between a container and covers that compose a decompression chamber can be omitted. A degasifier includes a decompression chamber provided with a container and covers, and a gas-permeable tube. The container is a tubular body extending along the central axis. The covers seal the openings of the ends of the tubular body. The gas-permeable tube is contained in the decompression chamber in such a manner that a liquid to be degassed that has entered from the outside of the decompression chamber flows therethrough and the liquid to be degassed that has flowed therethrough flows out of the decompression chamber. The inner circumference surfaces in the vicinities of the openings of the container each are provided with a first slope that is formed to be tilted at a predetermined angle .theta. with respect to the central axis and to extend away from the central axis toward the opening side of the container. A portion of each of the covers that is in contact with the container is provided with a second slope that is formed to be tilted at the angle .theta. with respect to the central axis and to extend to approach the central axis toward the inner side of the decompression chamber, with the openings being sealed. The openings are sealed with the container and the covers being joined to each other in the state where the first slopes and the second slopes are in contact with each other, respectively.