Disclosed herein is a lens mechanism including: a base; a guide member fixed to the base; a lens holding member adapted to hold the lens and which is held by the guide member in such a manner as to move straight along the optical axis; a rotary member adapted to rotate while at the same time engaging with part of the lens holding member so as to cause the lens holding member to move straight along the optical axis; and polymer actuator elements each of which has one end fixed to the base or guide member and the other end engaging with part of the rotary member so as to rotate the rotary member in a plane orthogonal to the optical axis.