A liquid-cooled-type cooling device comprising a casing which has a top wall, a bottom wall, and a peripheral wall, which has a cooling-liquid inlet and a cooling-liquid outlet formed thereon, and in which a cooling-liquid flow channel is provided between the cooling-liquid inlet and the cooling-liquid outlet, wherein a plurality of fins projecting into the cooling-liquid flow channel and extending in a flow direction of cooling liquid within the cooling-liquid flow channel are provided on an inner surface of a portion of a wall selected from the top wall and the bottom wall of the casing onto which a heat-generating body is attached such that the heat-generating body is in contact with an outer surface of the selected wall, the portion of the selected wall facing the cooling-liquid flow channel, and the plurality of fins being spaced from one another in a width direction of the cooling-liquid flow channel; each of the fins has a wavy shape as viewed on a cross section taken along a horizontal plane perpendicular to a height direction of the fins, and has wave crest portions and wave trough portions alternately formed thereon; the fins are configured and arranged such that the cooling liquid flows between two adjacent fins while meandering; a first fin of two adjacent fins (16A, 16B) is configured such that two lines of intersection formed between the horizontal plane and second-fin-side surfaces of two slant portions connecting two adjacent wave crest portions and a wave trough portion located therebetween intersect each other at a point located on a first straight line; the wave crest portions and the wave trough portions of each fin are rounded; and, as viewed on the horizontal plane, the point at which the two lines of intersection between the horizontal plane and the second-fin-side surfaces of the two slant portions intersect each other is located at a position at which imaginary lines extending toward the second fin from the second-fin-side surfaces of the two slant portions intersect each other; a second fin of the two adjacent fins (16A, 16B) is configured such that two lines of intersection formed between the horizontal plane and first-fin-side surfaces of two slant portions connecting two adjacent wave trough portions and a wave crest portion located therebetween intersect each other at a point located on a second straight line; the first straight line is located on a side toward the second fin in relation to the second straight line, and as viewed on the horizontal plane, the first straight line intersects only with the second fin, and a set of two adjacent fins (16A, 16B) is provided adjacent to another set of two adjacent fins so that the first straight line of a first set of fins is located between the second straight line of the first set of fins and the second straight line of a second set of fins, characterized in that a first fin has a surface facing a second fin such that two lines of the surface extended from two slant portions of the first fin converge to intersect each other at a point located beyond the trough portion of the first fin, and respective points associated with each trough portion of the first fin are located on a side toward the first fin in relation to the center portion between the trough portion of the first fin and the trough portion of the second fin adjacent to the first fin, and a second fin has a surface facing a first fin such that two lines of the surface extended from two slant portions of the second fin converge to intersect each other at a point located beyond the wave crest of the second fin, and respective points associated with each wave crest of the second fin are located on a side toward the second fin in relation to the center portion between the wave crest of the second fin and the wave crest of the first fin adjacent to the second fin.