A pharmaceutical composition including, as an active ingredient, one of the following proteins (I) and (II): (I) an apoptosis inhibitor of macrophage; and (II) a protein which consists of an amino acid sequence having deletion, substitution, or addition of one or more amino acids in an amino acid sequence of the apoptosis inhibitor of macrophage and having homology to the amino acid sequence of the apoptosis inhibitor of macrophage, and has a function of inhibiting the differentiation of preadipocytes to mature adipocytes and/or a function of inducing lipolysis in the mature adipocytes.