this embodiment the cap 5 is formed separately but it can be formed by a series of multi color molding in the same way as the other parts are formed a finished pump shown in fig2 is obtained by forming the cap 5 additionally to the piston pump in fig1 fig7 is a sectional view of a piston pump 9 in the embodiment 2 where a second check valve 4 is constituted in the cylinder 1 of the above described embodiment 1 to prevent a reversed flow of ink from the cylinder space 1 c at the sucking side to the recording head 6 the second check valve 4 is formed out of a combination of an insoluble resin material with that of the cylinder 1 by the insert molding or the multi color molding as shown in fig7 hereinafter a sucking movement of the recording head is explained by referring to fig8 to 10 in these figures a numeric character 6 stands for a recording head 5 stands for a cap tightly attached to the recording head to form a closed system and usually formed out of an elastic material such as a rubber an elastomer etc the pump unit 10 in the second embodiment is fixed to the cap 5 fig8 illustrates a sucking status where the piston 2 is connected with the unshown deriving.