A power conversion device includes: a cooling base 5 in which a flow passage 51 through which a cooling medium flows is formed and an opening portion 50 which is communicated with the flow passage 51 is formed; a power module 1; and a flow passage control portion 16b. The power module 1 has a bottomed cylindrical portion 13a in which a power semiconductor element is housed and which is inserted into the flow passage 51 through the opening portion 50, a flange portion 13b which is formed on an opening of the cylindrical portion 13a and is fixed to the cooling base 5 so as to close the opening portion 50, and a group of radiator fins 144 which are mounted on an outer peripheral surface of the cylindrical portion 13a with a gap of a predetermined distance formed between the flange portion 13b and the group of radiator fins 144. The flow passage control portion 16b is arranged in a gap formed between the flange portion 13b and the group of radiator fins 144, and introduces the cooling medium into the group of radiator fins 144 while preventing the cooling medium from flowing into gaps 51c.