A wireless LAN module as a composite module according to the present invention includes a first substrate 26 and a second substrate 28 that is so disposed as opposed to the other principal surface 48b of the first substrate 26. An external connector 66 for the connection with an electronic apparatus is mounted on one principal surface 48a of the first substrate 26. An electronic component device 76a is mounted on one principal surface of the second substrate 28 in a region opposing the external connector 66 sandwiching the first substrate 26 therebetween. A heat dissipation member 78 is disposed on a surface which is an opposite side to the mounting-surface of the electronic component device 76a.