A sealed mixer comprises a housing provided with a mixing chamber and a material insertion port for inserting materials into the mixing chamber; a weight for pressing the materials inserted into the material insertion port toward the mixing chamber; and a shaft member which extends upward from the weight and moves upward and downward together with the weight, the weight being connected to a lower end portion of the shaft member, a reservoir adapted to store lubricant between the weight and the shaft member is formed at a part connecting the weight and the shaft member, and a lubricant supply path adapted to supply the lubricant from an outside toward the reservoir is formed in the shaft member.