NOVELTY - The unit (1) has thermoelectric devices (2a) in contact with inner surfaces of substrates (2b,2c) that cover the recesses (41p,51p) defining flow passages (46a,56b) within the cases (40,50). The accommodating recesses (41k,51k) are formed in opposed portions (41n,51n) of cases. The elastic plate-like segments (8,9) housed in accommodating recesses, are in contact with both the bottom portion of accommodating recesses and the outer surface of substrates. The distance (L1) set between the opposed portions by metal tubes (45,55), is longer than distance (L2) between substrate outer surfaces.    USE - Thermoelectric conversion unit of heat exchange system used for heating or cooling of interior of vehicle, for heating or cooling of vehicle components such as battery, and for air conditioning of interior of vehicle. Can also be used in heating or cooling of other products.    ADVANTAGE - The flow direction of the coolant fluid in one case is opposed to the flow direction of the coolant fluid in other case, so that a difference between the heat absorption side and heat dissipation side of the thermoelectric module is small between the thermoelectric modules. Thus, the overall thermal efficiency is high. The thermoelectric module can be held rotationally in the thermoelectric conversion unit. The thermoelectric devices provided between the substrates are prevented from damage by the biding power of the connectors that connect the cases. The elastic plate-like segments can elastically hold the substrates where the thermoelectric devices are provided between the substrates in both thickness directions, so that the external forces are inhibited from being applied to the thermoelectric devices. The elastic plate-like segments provide fluid tightness between the cases and substrates. The release of connector from the cases is avoided.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of the thermoelectric conversion unit.    Thermoelectric conversion unit (1)    Thermoelectric device (2a)    Substrates (2b,2c)    Elastic plate-like segments (8,9)    Cases (40,50)    Accommodating recesses (41k,51k)    Opposed portions of cases (41n,51n)    Recesses (41p,51p)    Metal tubes (45,55)    Flow passages (46a,56b)    Distance between opposed portions (L1)    Distance between outer surface of substrates (L2)