To obtain an arteriosclerosis-preventing agent which can prevent atheromatous arteriosclerosis and further reduce and control the advance of the atheromatous arteriosclerosis, and a food or medicine containing the arteriosclerosis-preventing agent.

This arteriosclerosis-preventing agent is characterized by containing a mycelium extract extracted from the mycelium culture product of Cortinellus shiitake, and a food or medicine contains the arteriosclerosis- preventing agent. The extract is desirably an extract which is obtained by inoculating Cortinellus shiitake fungus in a solid culture medium containing bagasse as a main material, proliferating the mycelia, disintegrating the obtained mycelium-containing solid culture medium, adding water and one or more enzymes selected from cellulases and proteases to the disintegrated solid medium at a temperature of 30 to 50°C, crushing or grinding the solid culture medium in the presence of the enzymes, extracting the Cortinellus shiitake mycelia, and then deactivating or sterilizing the obtained extract at a temperature of ≤95°C.