An object of the present invention is to provide a microorganism strain that accumulates a high molecular weight PHA, and a PHA production method using the microorganism. The present invention provides a method for producing a PHA copolymer, which includes culturing a microorganism, wherein at least a portion of either of the following genes (a) and (b) of the microorganism has been altered by substitution, deletion, insertion, and/or addition to reduce or eliminate the activity of a PHA degrading enzyme encoded by the gene: (a) a PHA degrading enzyme gene encoding the amino acid sequence of SEQ ID NO:2 in the sequence listing; and (b) a gene encoding a polypeptide having at least 85% sequence identity to the amino acid sequence of SEQ ID NO:2 in the sequence listing and having PHA degrading enzyme activity.