The invention relates to a back massaging device. The back massaging device comprises a sliding chute rail, a transmission part, a motor, a sliding bracket and a vibrator, wherein the sliding bracket is connected with a massaging pillar and a massaging shaft; a spring seat is arranged outside the massaging pillar; a support spring I sleeves the exterior of the massaging pillar; a limiting block is arranged on the support spring I; a support spring II sleeves the massaging pillar; a cavity is formed in the massaging pillar; the lower end of the massaging pillar is connected with a liquid discharging pipeline; a runner I and a runner II are arranged on the massaging shaft; a liquid discharging hole is sealed by using a sealing block; the sealing block is used for fixing a connection rod I; the connection rod I is connected with a connection rod II; a support plate is arranged in the cavity; a spring I is fixed in the cavity and is connected with a rubber ball; a magnet I slides on the side wall of the cavity; a magnet II is arranged inside the limiting block; a spring II is fixed on the support plate and is connected with a pressing block. According to the back massaging device, two springs and the limiting block are used for buffering the pressing force; the liquid discharging hole is automatically opened and closed while the limiting block moves up and down; massaging oil is automatically coated.