A fixed quantity discharge device for a liquid container, the fixed quantity discharge device for a liquid container comprising: a container body wherein contents are kept; and a piston which moves according to usage of the contents inside the container body; and pipette part detachably combined from the container body, and provided with a pipette pipe which sucks and discharges a fixed amount of contents contained in the container body; and a support body combined encircling an upper portion of the container body, the support body further comprising: a coupling part to which the pipette pipe is combined, and provided with a contents suction tube, at an inner side of the coupling part, extending into an interior of the container body for the pipette pipe to be inserted and withdrawn and further comprising a contents inflow hole at an lower end thereof, the pipette pipe sucking and discharging contents flowing into the contents suction tube; and a sealing member installed at an inner lower end of the contents suction tube and guiding contents flowing in through the contents inflow hole to move to the pipette pipe only; wherein the pipette part comprising: an inner cap combined with screw coupling, further comprising a guide part which ascends and descends a button part; an outer cap combined encircling the inner cap and rotating with the inner cap, further comprising a vertical guide groove formed longitudinally at an inner circumferential surface so as to guide a vertical movement of the button part; and the button part ascending by rotation of the outer cap and descending by a user's pressurization, further comprising a guide protrusion which ascends and descends along the guide part of the inner cap. a container body wherein contents are kept; and a piston which moves according to usage of the contents inside the container body; and pipette part detachably combined from the container body, and provided with a pipette pipe which sucks and discharges a fixed amount of contents contained in the container body; and a support body combined encircling an upper portion of the container body, the support body further comprising: a coupling part to which the pipette pipe is combined, and provided with a contents suction tube, at an inner side of the coupling part, extending into an interior of the container body for the pipette pipe to be inserted and withdrawn and further comprising a contents inflow hole at an lower end thereof, the pipette pipe sucking and discharging contents flowing into the contents suction tube; and a sealing member installed at an inner lower end of the contents suction tube and guiding contents flowing in through the contents inflow hole to move to the pipette pipe only; wherein the pipette part comprising: an inner cap combined with screw coupling, further comprising a guide part which ascends and descends a button part; an outer cap combined encircling the inner cap and rotating with the inner cap, further comprising a vertical guide groove formed longitudinally at an inner circumferential surface so as to guide a vertical movement of the button part; and the button part ascending by rotation of the outer cap and descending by a user's pressurization, further comprising a guide protrusion which ascends and descends along the guide part of the inner cap. a coupling part to which the pipette pipe is combined, and provided with a contents suction tube, at an inner side of the coupling part, extending into an interior of the container body for the pipette pipe to be inserted and withdrawn and further comprising a contents inflow hole at an lower end thereof, the pipette pipe sucking and discharging contents flowing into the contents suction tube; and a sealing member installed at an inner lower end of the contents suction tube and guiding contents flowing in through the contents inflow hole to move to the pipette pipe only; wherein the pipette part comprising: an inner cap combined with screw coupling, further comprising a guide part which ascends and descends a button part; an outer cap combined encircling the inner cap and rotating with the inner cap, further comprising a vertical guide groove formed longitudinally at an inner circumferential surface so as to guide a vertical movement of the button part; and the button part ascending by rotation of the outer cap and descending by a user's pressurization, further comprising a guide protrusion which ascends and descends along the guide part of the inner cap. an inner cap combined with screw coupling, further comprising a guide part which ascends and descends a button part; an outer cap combined encircling the inner cap and rotating with the inner cap, further comprising a vertical guide groove formed longitudinally at an inner circumferential surface so as to guide a vertical movement of the button part; and the button part ascending by rotation of the outer cap and descending by a user's pressurization, further comprising a guide protrusion which ascends and descends along the guide part of the inner cap.