To provide an element with variable characteristic such as a mirror with variable focus in which the focus can be varied along any axis except the center axis of the mirror and a plurality of focuses can be formed, and to provide an actuator and an actuator system suitable for the element.

A large number of linear actuators 7 are distributed and disposed on the back side of the reflection face of a mirror and connected to the back face side so that driving of the linear actuators 7 is controlled to control the reflection face as an active curved face 5a into any form and that the focus position and the number of focuses of the mirror can be varied.