Manufacturing method for 7-dehydrocholesterol and vitamin d3

The present invention provides a method for manufacturing 7-dehydrocholesterol, the method being characterized by deleting, replacing or adding at least one base in a gene that is present on the chromosomal DNA in a parent strain and that codes a protein having 7-dehydrocholesterol reduction activity, whereby a labyrinthulean micro-organism that has decreased 7-dehydrocholesterol reduction activity in comparison to the parent strain or no 7-dehydrocholesterol reduction activity, and that produces 7-dehydrocholesterol is cultured in a culture medium, 7-dehydrocholesterol is generated in the culture, accumulated and then harvested from the culture medium. Also provided is a method for manufacturing vitamin D3, the method being characterized in that UV light is shone onto 7-dehydrocholesterol manufactured by the aforementioned manufacturing method.