[Problem] To provide a mitochondria-function regulator effective for treatment or prevention of obesity, and a screening method therefore. [Solution] The mitochondria-function regulator of the present invention contains, as an active ingredient, a PGC-1² - protein function regulator synoviolin. The screening method of the present invention includes a step for causing a test substance to act on an adipose tissue cell or an individual animal, and measuring or detecting one or more of the following in the adipose tissue cell: (1) expression level of synoviolin； (2) a bond between synoviolin and PGC-1² protein； and (3) the ubiquitination of the PGC-1² protein by synoviolin.
