The invention relates to an oil supply device which comprises a machine frame. The machine frame is provided with an oil tank, a first piston mechanism and a driving mechanism. The first piston mechanism comprises a first piston cylinder, a first piston and a first piston rod. The first piston is in sealed sliding connection with the interior of the first piston cylinder, the first piston rod is fixedly connected to the first piston, an oil inlet pipe is connected between the first piston cylinder and the oil tank, the oil inlet pipe is provided with a first one-way valve, the first piston cylinder is connected with an oil drainage mechanism, a brush is connected to the oil drainage mechanism, and the oil drainage mechanism is provided with a second one-way valve. The driving mechanism comprises an inner gear ring and a gear, the gear is engaged with the inner gear ring, a first connection rod is fixedly connected to the gear, the end, away from the gear, of the first connection rod isused for being detachably connected with a chain wheel, a second connection rod is fixedly connected to the gear, and the end, away from the gear, of the second connection rod is rotationally connected to the first piston rod. By means of the scheme, a chain is automatically coated with oil.