The process of the present invention for producing a polyester resin comprising
a dicarboxylic acid constitutional unit and a diol constitutional unit having a
cyclic acetal skeleton comprises a step (1) of subjecting a diol (A) having a cyclic
acetal skeleton and an ester (D) to transesterification reaction and a step (2)
of mainly converting the resultant oligomer into a high polymer. The step (1) simultaneously
satisfies the requirements (i) to (iv) as described in the specification. In the
process of the present invention, the polyester resins having excellent moldability
and mechanical properties are stably produced by a transesterification method which
is less detrimental to environments.
