PURPOSE: To readily obtain the subject spherical oligomer having high sphericity and capable of readily handling by stirring polycarbonate oligomer powder in a granulation vessel, feeding an organic solvent thereto, evaporating the organic solvent while bringing the organic solvent into contact with powder.

CONSTITUTION: Polycarbonate oligomer powder is fed into a granulation vessel A equipped with an agitator 1 having an agitating blade 2 and a jacket 3 for temperature control and an organic solvent solution B of a polycarbonate oligomer and as necessary, a crystallizing agent are added thereto while previously stirring this oligomer powder by the agitator 1 and the organic solvent is evaporated while bringing this organic solvent solution B into contact with polycarbonate oligomer powder to granulate the powder into sphere. The evaporated organic solvent is fed to a solvent-recovering apparatus D and the resultant spherical oligomer G is taken out through a valve 4, dried by a drier E, fed to a solid phase polymerizer H and subjected to solid phase polymerization, discharged through a valve 6 to provide the object crystalline polycarbonate oligomer having 0.8-1.0 sphericity expressed in terms of sphericity of Wadell.