An object of the present invention is to provide polybutylene terephthalate which has excellent color tone, hydrolysis resistance, heat stability, transparency and moldability as well as a less content of impurities, can be produced with maintaining its productivity while preventing from generation of tetrahydrofuran as a by-product, and can be suitably applied to films, monofilaments, fibers, electric and electronic parts, automobile parts, etc.In an aspect of the present invention, there is provided a process for continuously producing polybutylene terephthalate from terephthalic acid and 1,4-butanediol in a presence of a catalyst comprising a titanium compound and a compound of at least one metal selected from Group 1 and Group 2 of the Periodic Table, which process satisfies such the following requirements (a) to (c) that: (a) an oligomer is obtained by conducting a continuously esterification reaction of terephthalic acid and 1,4-butanediol in the presence of titanium catalyst in an amount of not more than 460 μmol as a titanium atom based on 1 mol of terephthalic acid unit; (b) polycondensation reaction of the said oligomer is continuously conducted in the presence of compound of at least one metal selected from Group 1 and Group 2 of the Periodic Table as the catalyst in an amount of not more than 450 μmol as the metal atom based on 1 mol of terephthalic acid unit; and (c) the said compound of at least one metal may be added to a stage before obtaining an oligomer having esterification conversion of not less than 90% in an amount of not more than 300 μmol as the metal atom based on 1 mol of terephthalic acid unit, and the said compound of at least one metal may be added to a stage on or after obtaining an oligomer having esterification conversion of not less than 90% in an amount of not less than 10 μmol as the metal atom based on 1 mol of terephthalic acid unit.