PURPOSE: To easily attain high-density information writing and reading by forming a metallic film on the surface of an electret body and etching the metallic film partially.

CONSTITUTION: An electret 2 is formed in the form of a film on the surface of a substrate 1 made of metal or glass, plastic or the electret main body when the substrate 1 is not the electret, a metallic film of aluminum, tungsten, etc., which is about 0.1μm in thickness is formed on the electret 2 and by a normal photo-etching method, for example, by such a method as making holes about 0.1μm in diameter at the intervals of about 0.1μm in the metallic film 3, information is written and stored. In this case, the potential difference to the metallic film can be obtained large, the tip diameter of the needle of a probe can be minimized to 0.1μm or below and the high-density information writing and reading can be easily attained.