A thermoplastic aromatic polysulfone is obtained by polymerizing a dihalogeno compound (A) and a dihydric phenol (B). The ratio (Mw/Mn) between a number average molecular weight (Mn) and a weight average molecular weight (Mw) is at least 1.80 and less than 1.90, and the number average molecular weight (Mn) is at least 6,000 and less than 14,000. In (A) and (B), each of X and X′ independently represents a halogen atom; each of R1, R2, R3 and R4 independently represents an alkyl group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms; each of n1, n2, n3 and n4 independently represents an integer of 0 to 4; and when n1, n2, n3 or n4 is an integer of 2 to 4, a plurality of R1, R2, R3 or R4 groups may be the same or different from each other.