Joined body

A joined body comprising:

• a main body section including a wall section, the wall section forming a passage along which a medium for accelerating heat exchange flows;
• and
• a cover configured to cover a surface of the main body section on which the passage is formed, the cover including:
• a covering section provided on a side facing the main body section and configured to cover the surface of the main body section on which the passage is formed;
• a groove section provided on the side facing the main body section and configured to accommodate an end portion of the wall section;
• and
• a stirred joint section provided on a side opposite to a side on which the covering section and the groove section are provided, the stirred joint section being at least partly frictionally stirred by a depth reaching a bottom of the groove section from a surface on a side opposite to the side facing the main body section, and the stirred joint section being bonded to the end portion of the wall section,
• wherein only a portion of the cover is stirred as long as the main body section and the cover can be bonded together, and
• wherein a relation 1<T1/T2<3 is satisfied,
• where T1 denotes a thickness of the cover and T2 denotes a depth of the groove section, and
• the stirred joint section is formed by being stirred by a depth of T1−T2 from a surface opposite to the side on which the groove sections are formed to prevent deformation of the passage.