A lubricator includes a pump body configured to include a cylinder, an inlet passage, a first outlet passage and a second outlet passage, a piston configured to include an inlet port, a circumferential groove and an inner passage, and inserted into the cylinder, first to fourth check valves provided on the inlet side of the inlet passage, the outlet sides of the first and second outlet passages and the inner passage of the piston, a lubricant containing unit connected to the first check valve, and a piston driving unit configured to reciprocate the piston.