Armature and armature driving device

This invention is an armature and an armature driving device in which the armature is rotated around its axis so as to inhibit uneven wear from occurring between the armature and a housing. That is, an armature which is slidably provided within a housing filled with fluid and which divides the inside of the housing into two fluid chambers is further provided with a communicating hole that enables the fluid to pass between the two fluid chambers. This communicating hole is formed such that the fluid passing through the communicating hole and out from the armature when the armature slides flows out at an angle to, and to the side of, a center axis of the armature.