To provide a shell and tube heat exchanger having structural strength which is sufficient enough even to receive an effect of a water hammer phenomenon or the like, and capable of miniaturizing an overall size.

A tabular member 44 is brazed on one end sides of a multiplicity of thin tubes 43, and the thin tubes are communicated with a recessed part 441. Tabular members 45 and 46 are similarly brazed on other end sides, half of the thin tubes is communicated with a recessed part 451, and another half of the thin tubes is communicated with a recessed part 461. The thin tubes and the tabular members are inserted between both left and right side walls 412 and 413 of a body case 41, and circumferential rim flanges 442, 452 and 462 of each tabular member are brazed on each side wall to provide a constrained state between both side walls. Inflow water from a connection opening 48b passes through the thin tubes from an inflow header 48, it reaches a turn around header 47, it passes the thin tubes once again, it reaches an outflow header 49, and it is discharged from a connection opening 49b.