A cap (10) of a Hypsizygus marmoreus cultivation bottle, said cap being provided with a tubular member (20) fitting into a wide mouth (54) of the cultivation bottle (50), wherein: the tubular member (20) comprises a large-diameter tubular part (22), which covers the end edge of the wide mouth (54) and the outer side surface in the vicinity of the end edge and fits thereinto, a small-diameter tubular part (24), which is provided with a first opening (21) having a smaller diameter than the large-diameter tubular part (22) and positioned closer to the center, and a connection part (25), which connects the outer peripheral edge of the large-diameter tubular part (22) and the small-diameter tubular part (24); and the height of the inner side surface (15) of the small-diameter tubular part (24) is 6-30 mm inclusive.
