A semiconductor element cooling structure includes first and second semiconductor elements; a heat sink having a mounting surface on which the semiconductor elements are mounted and a cooling medium channel formed inside, through which a cooling medium for cooling the semiconductor elements flows; and a protruded portion provided at a position opposite to the mounting surface of the heat sink, extending in a direction intersecting flow direction of the cooling medium (direction of arrow DR1) and protruding from a bottom surface of the cooling medium channel to the inside of cooling medium channel. The semiconductor elements are arranged side by side in the direction of arrow DR1, such that the first semiconductor element is positioned upstream side than the second semiconductor element. A protruded portion for the second semiconductor element is provided to be positioned on the downstream side of first semiconductor element and upstream side than the center of second semiconductor element in the direction of arrow DR1.