PROBLEM TO BE SOLVED: To solve a problem that the production of a compost culture medium for culturing Agaricus blazei Murill requires much labor and increases the production cost, because the compost culture medium in the conventional culture of Agaricus blazei Murill is self produced. SOLUTION: Since an existing compost is reproduced into a culture medium for culturing the Agaricus blazei Murill, the production cost can be reduced.