A structure of a heat exchanger core without a header plate, in which: a pair of plates having a pair of side walls extended upward on both sides, respectively, to form a whole body into a groove shape, and bulging portions formed at edges on both open sides of a groove bottom on an outer side in a thickness direction orthogonally to the side walls are fitted with each other facing in a reverse direction, to thereby form a flat tube ; and a casing is fitted onto an outer periphery of a stacked body configured by stacking a plurality of the flat tubes on each other at the bulging portions , wherein: an external frame portion whose inner periphery matches with an outer periphery on a bulging portion side of the stacked body , an inside flange portion formed at a peripheral edge of the external frame portion , and a packing holding portion extended upward in a side wall direction at an inner edge of the inside flange portion constitute a frame body ; characterised in that the external frame portion of a pair of the frame bodies are fitted onto both ends on a bulging portion side of the stacked body to grasp outer peripheries at both end portions of the stacked body with the frame body , and the casing is fitted onto an outer periphery of the external frame portion of the frame body ; and as a result, an annular groove into which a packing for seal can be inserted is formed between a packing grasping portion of the frame body and both end edges of the casing . a pair of plates having a pair of side walls extended upward on both sides, respectively, to form a whole body into a groove shape, and bulging portions formed at edges on both open sides of a groove bottom on an outer side in a thickness direction orthogonally to the side walls are fitted with each other facing in a reverse direction, to thereby form a flat tube ; and a casing is fitted onto an outer periphery of a stacked body configured by stacking a plurality of the flat tubes on each other at the bulging portions , wherein: an external frame portion whose inner periphery matches with an outer periphery on a bulging portion side of the stacked body , an inside flange portion formed at a peripheral edge of the external frame portion , and a packing holding portion extended upward in a side wall direction at an inner edge of the inside flange portion constitute a frame body ; characterised in that the external frame portion of a pair of the frame bodies are fitted onto both ends on a bulging portion side of the stacked body to grasp outer peripheries at both end portions of the stacked body with the frame body , and the casing is fitted onto an outer periphery of the external frame portion of the frame body ; and as a result, an annular groove into which a packing for seal can be inserted is formed between a packing grasping portion of the frame body and both end edges of the casing . an external frame portion whose inner periphery matches with an outer periphery on a bulging portion side of the stacked body , an inside flange portion formed at a peripheral edge of the external frame portion , and a packing holding portion extended upward in a side wall direction at an inner edge of the inside flange portion constitute a frame body ; characterised in that the external frame portion of a pair of the frame bodies are fitted onto both ends on a bulging portion side of the stacked body to grasp outer peripheries at both end portions of the stacked body with the frame body , and the casing is fitted onto an outer periphery of the external frame portion of the frame body ; and as a result, an annular groove into which a packing for seal can be inserted is formed between a packing grasping portion of the frame body and both end edges of the casing . <EOS>