There is provides a heat exchanger comprising: a plurality of tubes (110)
stacked on each other; and a pair of header tanks (140), each header tank
(140) having a flow section (151) in which fluid flows, extending in a
direction of stack of the tubes (110), wherein both end sections (111) of
the tubes (110) in the longitudinal direction are joined to the pair of
header tanks (140), the flow section (151) of each header tank (140) and
the inside of each tube (110) are communicated with each other, a tip
position (a) of the tube end section (111) is arranged in an outside
region of the flow section (151), and an inner wall width size (b) of the
flow section (151) is smaller than a size (c) in the width direction of
the header tank (140) at the tube end section (111).