A heat recovery system configured to recover heat from emission of an internal combustion engine, the heat recovery system comprising: a tubular casing; a tube stack created by stacking multiple flat tubes, each being formed in a flat, substantially donut shape and being structured to have at least two non-contact areas that are not in contact with inside of the casing, wherein the multiple flat tubes are stacked in a stacking direction at preset stacking intervals defined by at least two communication paths (36, 37) and are interconnected in the stacking direction by means of the at least two communication paths (36, 37), such that the at least two non-contact areas of the multiple flat tubes are respectively aligned in sequence in the stacking direction and the at least two communication paths (36,37) are respectively aligned in sequence in the stacking direction; a heat exchange medium supply pipe connected with respective one communication paths of the at least two communication paths aligned in sequence in the tube stack, in order to supply a heat exchange medium; a heat exchange medium recovery pipe connected with respective other communication paths of the at least two communication paths aligned in sequence in the tube stack, in order to recover the heat exchange medium; an emission inflow-side end plate located at an emission inflow end of the tube stack on an emission inflow side of the casing and attached to the casing, so as to block respective one non-contact areas of the at least two non-contact areas aligned in sequence in the tube stack; an emission outflow-side end plate located at an emission outflow end of the tube stack on an emission outflow side of the casing and attached to the casing, so as to block respective other non-contact areas of the at least two non-contact areas aligned in sequence in the tube stack; an emission flow conduit inserted through inside of the tube stack to have a heat insulating effect and arranged to pass through the tube stack and make a flow of the emission; and a shutoff valve provided in the emission flow conduit to shut off the flow of the emission and release the shutoff of the flow of the emission. a tubular casing; a tube stack created by stacking multiple flat tubes, each being formed in a flat, substantially donut shape and being structured to have at least two non-contact areas that are not in contact with inside of the casing, wherein the multiple flat tubes are stacked in a stacking direction at preset stacking intervals defined by at least two communication paths (36, 37) and are interconnected in the stacking direction by means of the at least two communication paths (36, 37), such that the at least two non-contact areas of the multiple flat tubes are respectively aligned in sequence in the stacking direction and the at least two communication paths (36,37) are respectively aligned in sequence in the stacking direction; a heat exchange medium supply pipe connected with respective one communication paths of the at least two communication paths aligned in sequence in the tube stack, in order to supply a heat exchange medium; a heat exchange medium recovery pipe connected with respective other communication paths of the at least two communication paths aligned in sequence in the tube stack, in order to recover the heat exchange medium; an emission inflow-side end plate located at an emission inflow end of the tube stack on an emission inflow side of the casing and attached to the casing, so as to block respective one non-contact areas of the at least two non-contact areas aligned in sequence in the tube stack; an emission outflow-side end plate located at an emission outflow end of the tube stack on an emission outflow side of the casing and attached to the casing, so as to block respective other non-contact areas of the at least two non-contact areas aligned in sequence in the tube stack; an emission flow conduit inserted through inside of the tube stack to have a heat insulating effect and arranged to pass through the tube stack and make a flow of the emission; and a shutoff valve provided in the emission flow conduit to shut off the flow of the emission and release the shutoff of the flow of the emission.