A heat exchanger which, while having excellent heat exchanging performance, has a structure easy to produce, is of low cost, and has high quality and reliability. The heat exchanger has first base plates (26), in each of which first slits (30) and second slits (40) are provided in substantially parallel to each other, and has second base plates (28), in each of which third slits (50) with substantially the same shape as a first slit (30) are provided. The length in the longitudinal direction of a second base plate (28) is set to be less than the length of a second slit (40). The first base plates (26) and the second base plates (28) are layered over each other such that the first slits (30) provided in the first base plates (26) and the third slits (50) provided in the second base plates (28) are communicated. Flow paths (60) outside tubes are constructed by the first slits (30) provided in the first base plates (26) and the third base plates (50) provided in the second base plates (28). Flow paths (70) inside the tubes are constructed by the second slits (40) provided in the first base plates (26) and the second base plates (28). Since a heat exchanging section formed only by tubes can be constructed by the base plates with the slits, the heat exchanger can be easily produced. Further, the heat exchanger can be provided at low cost.