A novel organosilicon compound is provided as an organosilicon compound containing a β-ketoester structure that has minimal volatile components and generates a minimal amount of alcohol when used as a component within all manner of treatment agents. The organopolysiloxane is represented by an average composition formula shown below: YaR1bR2cSi(OR3)d(OH)eO(4-a-b-c-d-e)/2  (1) (wherein Y represents an organic group containing a β-ketoester group that may be at least partially enolized, R1 represents a monovalent hydrocarbon group that may optionally include a functional group such as a mercapto group, an epoxy group or a (meth)acryloyloxy group, R2 represents a monovalent hydrocarbon group that contains no functional groups, R3 represents a monovalent hydrocarbon group, and a, b, c, d and e are numbers that satisfy 0.01≦a≦1, 0≦b