PURPOSE: To obtain a sizing agent capable of simultaneously providing bundling properties, smoothness, opening properties and good adhesion to a matrix resin to carbon fibers.

CONSTITUTION: This sizing agent comprises a substance containing amino group without any active hydrogen in the structure, preferably a substance represented by the following formula: CH3(CH2)1N(CH2CH2O)mH(CH2CH-O)nH [(1)≥O; (m)≥1; (n)≥1].