Pump of electronically controlled brake system

1. A pump of an electronically controlled brake system comprising:

a bore formed in a modulator block and connected with a suction port and a discharge port; a piston installed in the bore in a reciprocating movable manner and defining an inlet path therein;

an inlet valve to open or close an exit-side end of the inlet path according to a position of the piston; and an outlet valve provided at one side of the bore, operations of the inlet and outlet valves being contrary to each other,

wherein the outlet valve comprises: a valve seat; a sleeve to surround the valve seat, said sleeve comprising an inner surface and an opposing outer surface; an outlet ball interposed between the inner surface of the sleeve and the valve seat and used to open or close a path defined in the valve scat; and a valve cap provided at the outer surface of the sleeve to isolate an interior from an exterior of the bore,

wherein the sleeve comprises an annular discharge groove formed on the outer surface to guide fluid, discharged by opening and closing operations of the outlet ball, to the outside, and

the sleeve comprises an orifice extending from the inner surface to the outer surface to introduce fluid into the discharge groove.