Polybutylene terephthalate is produced by continuously subjecting terephthalic acid and 1,4-butanediol to an esterification reaction in the presence of a titanium compound catalyst using one-stage or plural-stage esterification reaction vessel(s) and then subjecting the resultant reaction product to a polycondensation reaction, wherein the esterification reaction between terephthalic acid and 1,4-butanediol is conducted in the presence of a titanium compound having a specific concentration under a specific pressure at a specific molar ratio between the raw materials. The process avoids undesirable side reactions by continuously conducting esterification reaction using terephthalic acid as a raw material, and can minimize loss of raw materials.