A liquid waste processing apparatus having a liquid waste processing vessel for separating and recovering floating sludges. The liquid waste processing vessel includes an inlet disposed on its one side wall for receiving liquid wastes from above and turning them toward an exit disposed on the other side wall of the vessel, slanted downwardly toward the one side wall, and an inclined plate disposed above the exit for forming a shallow portion below the liquid surface and extended along the inclination of the opposite side wall toward the one side wall to define a narrow flow channel between the plate and the opposite side wall which is in communication from the bottom to the exit. The cross-sectional area of the narrow flow channel is made smaller than that of the channel opening. Floating sludges and precipitating sludges contained in liquid wastes from a coating booth, etc. can be separated and recovered completely and easily.