A molecular memory device has an insulating film with a cavity, the cavity having an upper portion and a lower portion; a first conductive member with a portion exposed at the lower portion of the cavity; a second conductive member with a portion exposed at the upper portion of the cavity; and a resistance varying-type molecular chain disposed in the cavity and bonded with the first conductive member or the second conductive member. The cavity is wider than at least one of the first conductive member along a first direction and the second conductive member along a second direction.