An electronic apparatus, comprising: an electronic component (21, 22); a closed circulating loop for circulating coolant; a heat receiver (28, 29) inserted in the closed circulating loop, the heat receiver (28, 29) having a thermal conductive plate received on the electronic component (21, 22); and a heat exchanger fixed onto a printed wiring board and inserted between a first connection tube and a second connection tube in the closed circulating loop so as to absorb heat from the coolant, wherein the heat exchanger comprises: a first plate; a second plate coupled to the first plate so as to define a coolant flow passage comprising a flat space between opposed front surfaces of the first plate and the second plate, the length of the flat space extending in a first direction, the width of the flat space extending in a second direction perpendicular to the first direction, and the thickness of the flat space extending in a third direction perpendicular to the plane defined by the first and second directions; a first metallic tube coupled to the first and second plates to form an inlet for inflow of the coolant into the flat space and coupled to the first connection tube; a second metallic tube coupled to the first and second plates to form an outlet for outflow of the coolant from the flat space and configured to be coupled to a second connection tube for connection in the closed circulating loop; first heat radiating fins standing from an outer surface of the first plate; and second heat radiating fins standing from an outer surface of the second plate, wherein a longitudinal axis of the first and second metallic tubes is coplanar with the plane defined by the first and second directions and is oriented in the first direction, the flat space extending further in the second direction than the first and second metallic tubes, the flat space extending further in the first direction than the second direction, the first heat radiating fins define airflow passages through which airflow runs in the second direction, thesecondheatradiatingfins defineairflowpassages through which airflow runs in the second direction, and an enlarged portion is defined between the first metallic tube and the flat space, the enlarged portion having a cross-section larger than the cross-section of the mouth of the flat space. an electronic component (21, 22); a closed circulating loop for circulating coolant; a heat receiver (28, 29) inserted in the closed circulating loop, the heat receiver (28, 29) having a thermal conductive plate received on the electronic component (21, 22); and a heat exchanger fixed onto a printed wiring board and inserted between a first connection tube and a second connection tube in the closed circulating loop so as to absorb heat from the coolant, wherein the heat exchanger comprises: a first plate; a second plate coupled to the first plate so as to define a coolant flow passage comprising a flat space between opposed front surfaces of the first plate and the second plate, the length of the flat space extending in a first direction, the width of the flat space extending in a second direction perpendicular to the first direction, and the thickness of the flat space extending in a third direction perpendicular to the plane defined by the first and second directions; a first metallic tube coupled to the first and second plates to form an inlet for inflow of the coolant into the flat space and coupled to the first connection tube; a second metallic tube coupled to the first and second plates to form an outlet for outflow of the coolant from the flat space and configured to be coupled to a second connection tube for connection in the closed circulating loop; first heat radiating fins standing from an outer surface of the first plate; and second heat radiating fins standing from an outer surface of the second plate, a first plate; a second plate coupled to the first plate so as to define a coolant flow passage comprising a flat space between opposed front surfaces of the first plate and the second plate, the length of the flat space extending in a first direction, the width of the flat space extending in a second direction perpendicular to the first direction, and the thickness of the flat space extending in a third direction perpendicular to the plane defined by the first and second directions; a first metallic tube coupled to the first and second plates to form an inlet for inflow of the coolant into the flat space and coupled to the first connection tube; a second metallic tube coupled to the first and second plates to form an outlet for outflow of the coolant from the flat space and configured to be coupled to a second connection tube for connection in the closed circulating loop; first heat radiating fins standing from an outer surface of the first plate; and second heat radiating fins standing from an outer surface of the second plate, wherein a longitudinal axis of the first and second metallic tubes is coplanar with the plane defined by the first and second directions and is oriented in the first direction, the flat space extending further in the second direction than the first and second metallic tubes, the flat space extending further in the first direction than the second direction, the first heat radiating fins define airflow passages through which airflow runs in the second direction, thesecondheatradiatingfins defineairflowpassages through which airflow runs in the second direction, and an enlarged portion is defined between the first metallic tube and the flat space, the enlarged portion having a cross-section larger than the cross-section of the mouth of the flat space.