A heat exchanger comprising: a plurality of heat exchange units (10, 11) each including a plurality of heat transfer tubes (12, 22) through which a refrigerant in a gas-liquid two-phase state flows and a plurality of fins (11, 21) arranged such that air passes between adjacent fins (11, 21) in an air passing direction, the heat transfer tubes (12, 22) being arranged at multiple levels in a level direction perpendicular to the air passing direction, the heat exchange units (10, 11) being arranged in multiple rows in a row direction, serving as the air passing direction; and a row straddling header, wherein the heat exchange units (10, 11) at opposite ends in the row direction of the heat exchange units (10, 11) arranged in the multiple rows serve as an inlet heat exchange unit into which the refrigerant flows and an outlet heat exchange unit out of which the refrigerant flows, wherein first ends of the heat transfer tubes (12, 22) being arranged at the multiple levels of adjacent heat exchange units (10,11) in the row direction of the heat exchange units (10, 11) arranged in the multiple rows are in communication with the row straddling header to provide refrigerant passages through which the refrigerant flows such that the refrigerant flowing from inlets of the heat transfer tubes being arranged at the multiple levels of the inlet heat exchange unit turns in the row straddling header to outlets of the heat transfer tubes being arranged at the multiple levels of the outlet heat exchange unit, wherein the row straddling header has an interior separated into a plurality of chambers arranged in a vertical direction, which is the level direction, and each of the refrigerant passages is isolated for its corresponding chamber, wherein an inlet header is disposed at ends of the heat transfer tubes being arranged at the multiple levels which serve as inlets when the heat exchanger is used as an evaporator, the inlet header is arranged so as to extend in the vertical direction and divides the refrigerant into multiple levels of the heat transfer tubes to flow in, characterized in that each of the inlet header and the row straddling header has an interior separated into a plurality of chambers arranged in the level direction, each of the refrigerant passages being isolated by corresponding chambers in the inlet header and the row straddling header. a plurality of heat exchange units (10, 11) each including a plurality of heat transfer tubes (12, 22) through which a refrigerant in a gas-liquid two-phase state flows and a plurality of fins (11, 21) arranged such that air passes between adjacent fins (11, 21) in an air passing direction, the heat transfer tubes (12, 22) being arranged at multiple levels in a level direction perpendicular to the air passing direction, the heat exchange units (10, 11) being arranged in multiple rows in a row direction, serving as the air passing direction; and a row straddling header, wherein the heat exchange units (10, 11) at opposite ends in the row direction of the heat exchange units (10, 11) arranged in the multiple rows serve as an inlet heat exchange unit into which the refrigerant flows and an outlet heat exchange unit out of which the refrigerant flows, wherein first ends of the heat transfer tubes (12, 22) being arranged at the multiple levels of adjacent heat exchange units (10,11) in the row direction of the heat exchange units (10, 11) arranged in the multiple rows are in communication with the row straddling header to provide refrigerant passages through which the refrigerant flows such that the refrigerant flowing from inlets of the heat transfer tubes being arranged at the multiple levels of the inlet heat exchange unit turns in the row straddling header to outlets of the heat transfer tubes being arranged at the multiple levels of the outlet heat exchange unit, wherein the row straddling header has an interior separated into a plurality of chambers arranged in a vertical direction, which is the level direction, and each of the refrigerant passages is isolated for its corresponding chamber, wherein an inlet header is disposed at ends of the heat transfer tubes being arranged at the multiple levels which serve as inlets when the heat exchanger is used as an evaporator, the inlet header is arranged so as to extend in the vertical direction and divides the refrigerant into multiple levels of the heat transfer tubes to flow in, characterized in that each of the inlet header and the row straddling header has an interior separated into a plurality of chambers arranged in the level direction, each of the refrigerant passages being isolated by corresponding chambers in the inlet header and the row straddling header.