A laundry treating apparatus, comprising: a cabinet; a tub provided within the cabinet; a rotary tub provided within the tub in a rotatable manner; and a washing agent supply unit comprising a storage container for storing therein a liquid washing agent including liquid detergent or liquid softener and drawn out of the cabinet, a washing agent supply passage having one side connected to the storage container and another side connected to the tub, and washing agent pump provided in the washing agent supply passage to deliver the liquid washing agent, wherein the washing agent pump comprises: a passage forming member forming a passage of the liquid washing agent and a pressing space, and provided with an intake valve opening and closing an inlet port of the pressing space, and a discharge valve opening and closing an outlet port of the pressing space; a cylinder disposed at one side of the passage forming member to communicate with the pressing space; and a piston disposed within the cylinder in a reciprocating manner; characterized by: a residual quantity detecting unit provided with an air pocket communicating with the passage of the passage forming member and temporarily storing therein air and the liquid washing agent, and electrodes disposed within the air pocket to be contactable with the liquid washing agent, the residual quantity detecting unit detecting the residual quantity of the liquid washing agent, wherein the residual quantity detecting unit is disposed at an upstream side of the pressing space or a downstream side of the pressing space along a flowing direction of the liquid washing agent. a cabinet; a tub provided within the cabinet; a rotary tub provided within the tub in a rotatable manner; and a washing agent supply unit comprising a storage container for storing therein a liquid washing agent including liquid detergent or liquid softener and drawn out of the cabinet, a washing agent supply passage having one side connected to the storage container and another side connected to the tub, and washing agent pump provided in the washing agent supply passage to deliver the liquid washing agent, wherein the washing agent pump comprises: a passage forming member forming a passage of the liquid washing agent and a pressing space, and provided with an intake valve opening and closing an inlet port of the pressing space, and a discharge valve opening and closing an outlet port of the pressing space; a cylinder disposed at one side of the passage forming member to communicate with the pressing space; and a piston disposed within the cylinder in a reciprocating manner; a passage forming member forming a passage of the liquid washing agent and a pressing space, and provided with an intake valve opening and closing an inlet port of the pressing space, and a discharge valve opening and closing an outlet port of the pressing space; a cylinder disposed at one side of the passage forming member to communicate with the pressing space; and a piston disposed within the cylinder in a reciprocating manner; characterized by: a residual quantity detecting unit provided with an air pocket communicating with the passage of the passage forming member and temporarily storing therein air and the liquid washing agent, and electrodes disposed within the air pocket to be contactable with the liquid washing agent, the residual quantity detecting unit detecting the residual quantity of the liquid washing agent, wherein the residual quantity detecting unit is disposed at an upstream side of the pressing space or a downstream side of the pressing space along a flowing direction of the liquid washing agent. a residual quantity detecting unit provided with an air pocket communicating with the passage of the passage forming member and temporarily storing therein air and the liquid washing agent, and electrodes disposed within the air pocket to be contactable with the liquid washing agent, the residual quantity detecting unit detecting the residual quantity of the liquid washing agent, wherein the residual quantity detecting unit is disposed at an upstream side of the pressing space or a downstream side of the pressing space along a flowing direction of the liquid washing agent.