PURPOSE: To achieve a complete sealing by a method wherein a base plate is made by injection molding and magnetizing plastic magnet material with an ink flow passage formed in at least one side thereof, a lid plate is made of a highly magnetic material and adapted to be magnetically held on the base plate and a magnetic fluid is provided between the joining parts of these plates.

CONSTITUTION: A base plate 1 is formed by injection molding plastic magnet material and an ink flow passage 1a is formed in the one side thereof. A lid plate 2 consists of a highly magnetic thin plate such as perpalloy and silicon steel and an ink delivering mechanism consisting of piezoelectric element is fixed to the lid plate in registration with the ink flow passage 1a and the lid plate is placed on the base plate 1 so as to be magnetically held thereon. A magnetic fluid 3 is poured into the ink flow passage 1a of the base plate 1 with the lid plate 2 fixed thereto. After the ink flow passage is filled full, the magnetic fluid 3 is carried out therefrom by pouring the ink. As a result, the magnetic fluid 3 remains in the small gaps produced between the joining parts of the base plate 1 and the lid plate 2, whereby the adhesiveness therebetween is enhanced and whereby the gaps are clogged therewith to enhance the sealability of the ink flow passage 1a.