A plate fin includes a slit structure formed by cutting and raising a portion of the plate fin to form an opening facing a flow direction of a fluid and a waffle structure formed by bending a portion of the plate fin to form a protrusion having an angle-shaped cross section which protrudes in a stack direction and having a ridge substantially perpendicular to the air flow direction, and the waffle structure is disposed on the upstream side on the plate fins with respect to the slit structure and a slant length L1 on the upstream side of the waffle structure is smaller than a slant length L2 on the downstream side of the waffle structure.