A pump dispenser which precisely transmits trigger motion and enables stable operation of a piston section. The manually operable pump dispenser is mounted on a vessel wherein the liquid contained in the cylinder section is compressed with a piston section by the displacement of a trigger structure and is ejected through a nozzle orifice. The dispenser includes a base body fixed on the vessel orifice via a packing structure, a cylinder section and a vent cylinder section formed adjacent to each other on the base body, and a trigger structure including a trigger section, a valve casing section mounted on the base body, and a trigger guide section oscillating in the vent cylinder section.