A heat exchanger comprising: a plurality of flat tubes that stack in a direction vertical to a flow direction of refrigerant flowing inside thereof; a header to which the plurality of flat tubes is connected at one end; an inflow plate that separates a refrigerant inflow portion and a lower circulation portion provided above the refrigerant inflow portion in the header; a lower dividing plate that is arranged parallel to a stack direction of the plurality of flat tubes to divide the lower circulation portion into lower ascent path on an internal side and a lower descent path of an external side; a lower accessway that connects the lower ascent path and the lower descent path of the lower circulation portion between the inflow plate and the lower dividing plate; wherein the inflow plate includes an ejection hole that ejects refrigerant, on a leeward side and an internal side, the heat exchanger being characterized in that it further comprises a vertical dividing plate that separates the lower circulation portion and an upper circulation portion provided above the lower circulation portion in the header; an upper dividing plate that is extending parallel to the stack direction of the flat tubes, in an ascent path provided on at least part of a leeward side, and a descent path provided at least on a windward side of the upper circulation portion; an upper accessway that connects the ascent path and the descent path of the upper circulation portion; and in that the vertical dividing plate includes a first passing port that lets refrigerant through, on a leeward side and an internal side, and a second passing port that lets refrigerant through, at least on a windward external side. a plurality of flat tubes that stack in a direction vertical to a flow direction of refrigerant flowing inside thereof; a header to which the plurality of flat tubes is connected at one end; an inflow plate that separates a refrigerant inflow portion and a lower circulation portion provided above the refrigerant inflow portion in the header; a lower dividing plate that is arranged parallel to a stack direction of the plurality of flat tubes to divide the lower circulation portion into lower ascent path on an internal side and a lower descent path of an external side; a lower accessway that connects the lower ascent path and the lower descent path of the lower circulation portion between the inflow plate and the lower dividing plate; wherein the inflow plate includes an ejection hole that ejects refrigerant, on a leeward side and an internal side, the heat exchanger being characterized in that it further comprises a vertical dividing plate that separates the lower circulation portion and an upper circulation portion provided above the lower circulation portion in the header; an upper dividing plate that is extending parallel to the stack direction of the flat tubes, in an ascent path provided on at least part of a leeward side, and a descent path provided at least on a windward side of the upper circulation portion; an upper accessway that connects the ascent path and the descent path of the upper circulation portion; and in that the vertical dividing plate includes a first passing port that lets refrigerant through, on a leeward side and an internal side, and a second passing port that lets refrigerant through, at least on a windward external side.