A heat exchanger comprising: a plurality of rectangular core plates (5, 6) stacked; a plurality of plate oil flow passages and a plurality of plate coolant flow passages alternatingly formed between the plurality of the core plates (5, 6); a plurality of rectangular fin plates (9, 10) each disposed at least to one flow passage of the plurality of the plate oil flow passages and the plate coolant flow passages; the core plates each including a pair of oil holes and a pair of coolant holes; in a case where a first reference line and a second reference line are defined as lines which pass through a center of the fin plate (9, 10), and which are perpendicular to each other in a plane of each of the core plates (5, 6), each of the fin plates (9, 10) having an anisotropy in which a passage resistance in a direction parallel to the first reference line is smaller than a passage resistance parallel to the second reference line, the pair of the oil holes being positioned on an outer edge of one of the core plates, the pair of the oil holes being positioned at symmetrical positions with respect to the center of the one of the core plates (5, 6) to sandwich the center of the one of the core plates (5, 6), and the pair of the oil holes being positioned to sandwich one of the fin plates (9, 10) along the first reference line, and the pair of the coolant holes being positioned on the outer edge of the one of the core plates (5, 6), the pair of the coolant holes being positioned at symmetrical positions with respect to the center of the one of the core plates (5, 6) to sandwich the center of the one of the core plates (5, 6), and the pair of the coolant holes being positioned to sandwich the one of the fin plates (9, 10) along the first reference line, wherein the pair of the oil holes are positioned on a diagonal line of one of the core plates (5, 6); and the pair of the coolant holes are positioned on a diagonal line of the one of the core plates (5, 6) which is different from the diagonal line on which the pair of the oil holes are formed, and the heat exchanger being characterized in that each of the fin plates (9, 10) is disposed in one flow passage of the plate oil flow passages and the plate coolant flow passages; and each of the core plates (5, 6) includes a plurality of protrusions each of which extends in a direction parallel to the first reference line within the one of the plate flow passages in which one of the fin plates is not disposed, the protrusions being formed in a region in which the protrusions are superimposed with a region in which the first fin plate is disposed. a plurality of rectangular core plates (5, 6) stacked; a plurality of plate oil flow passages and a plurality of plate coolant flow passages alternatingly formed between the plurality of the core plates (5, 6); a plurality of rectangular fin plates (9, 10) each disposed at least to one flow passage of the plurality of the plate oil flow passages and the plate coolant flow passages; the core plates each including a pair of oil holes and a pair of coolant holes; in a case where a first reference line and a second reference line are defined as lines which pass through a center of the fin plate (9, 10), and which are perpendicular to each other in a plane of each of the core plates (5, 6), each of the fin plates (9, 10) having an anisotropy in which a passage resistance in a direction parallel to the first reference line is smaller than a passage resistance parallel to the second reference line, the pair of the oil holes being positioned on an outer edge of one of the core plates, the pair of the oil holes being positioned at symmetrical positions with respect to the center of the one of the core plates (5, 6) to sandwich the center of the one of the core plates (5, 6), and the pair of the oil holes being positioned to sandwich one of the fin plates (9, 10) along the first reference line, and the pair of the coolant holes being positioned on the outer edge of the one of the core plates (5, 6), the pair of the coolant holes being positioned at symmetrical positions with respect to the center of the one of the core plates (5, 6) to sandwich the center of the one of the core plates (5, 6), and the pair of the coolant holes being positioned to sandwich the one of the fin plates (9, 10) along the first reference line, wherein the pair of the oil holes are positioned on a diagonal line of one of the core plates (5, 6); and the pair of the coolant holes are positioned on a diagonal line of the one of the core plates (5, 6) which is different from the diagonal line on which the pair of the oil holes are formed, and the heat exchanger being characterized in that each of the fin plates (9, 10) is disposed in one flow passage of the plate oil flow passages and the plate coolant flow passages; and each of the core plates (5, 6) includes a plurality of protrusions each of which extends in a direction parallel to the first reference line within the one of the plate flow passages in which one of the fin plates is not disposed, the protrusions being formed in a region in which the protrusions are superimposed with a region in which the first fin plate is disposed.