A lubricator comprising: an air bleeder configured to remove air out of a lubricant supply conduit, the air bleeder comprising: the lubricant supply conduit through which a lubricant is supplied to a mixing valve located in a machine tool; a lubricant tank in which the lubricant is stored; a branching portion located along the lubricant supply conduit; a return conduit connecting the branching portion and the lubricant tank to each other, wherein the lubricant supply conduit comprises a first supply conduit connecting the lubricant tank and the branching portion to each other, and a second supply conduit connecting the branching portion and the mixing valve to each other, and wherein at the branching portion, an upper-stream end of the return conduit is located above an upper-stream end of the second supply conduit; the mixing valve being configured to mix the lubricant and air together; an air supply conduit through which the air is supplied to the mixing valve; and a fluid mixture supply conduit which is located between the mixing valve and a lubrication target portion of the machine tool and through which a fluid mixture of the lubricant and the air is supplied to the lubrication target portion, wherein the second supply conduit, which connects the branching portion and the mixing valve to each other, has a length greater than a length of the first supply conduit, which connects the lubricant tank and the branching portion to each other. an air bleeder configured to remove air out of a lubricant supply conduit, the air bleeder comprising: the lubricant supply conduit through which a lubricant is supplied to a mixing valve located in a machine tool; a lubricant tank in which the lubricant is stored; a branching portion located along the lubricant supply conduit; a return conduit connecting the branching portion and the lubricant tank to each other, the lubricant supply conduit through which a lubricant is supplied to a mixing valve located in a machine tool; a lubricant tank in which the lubricant is stored; a branching portion located along the lubricant supply conduit; a return conduit connecting the branching portion and the lubricant tank to each other, wherein the lubricant supply conduit comprises a first supply conduit connecting the lubricant tank and the branching portion to each other, and a second supply conduit connecting the branching portion and the mixing valve to each other, and a first supply conduit connecting the lubricant tank and the branching portion to each other, and a second supply conduit connecting the branching portion and the mixing valve to each other, and wherein at the branching portion, an upper-stream end of the return conduit is located above an upper-stream end of the second supply conduit; the mixing valve being configured to mix the lubricant and air together; an air supply conduit through which the air is supplied to the mixing valve; and a fluid mixture supply conduit which is located between the mixing valve and a lubrication target portion of the machine tool and through which a fluid mixture of the lubricant and the air is supplied to the lubrication target portion, wherein the second supply conduit, which connects the branching portion and the mixing valve to each other, has a length greater than a length of the first supply conduit, which connects the lubricant tank and the branching portion to each other.