A polymer and a treating agent (such as a surface-treating agent) are provided that have excellent characteristics in such properties as water repellency, oil repellency, antifouling property and charge controlling property. The polymer contains a structural unit derived from fluorosilsesquioxane having an addition polymerizable group, or contains a structural unit derived from fluorosilsesquioxane having an addition polymerizable group and a structural unit derived from organopolysiloxane having an addition polymerizable group. The treating agent contains the polymer. An article treated with the treating agent is also provided.