A connecting structure includes a circuit board with a first connection land having a plurality of conductor patterns on the surface thereof, a second connection land disposed in a position opposite to the first connection land of the circuit board, and a flexible board including an insulating layer formed so as to surround at least a part of outer periphery of the second connection land. The first connection land and the second connection land are bonded to each other with a bonding member, and the insulating layer is thicker than the total thickness of the second connection land and the first connection land. It is possible to obtain an electronic circuit connecting structure which is free from short-circuit due to running of the bonding member such as solder even with the connecting land greatly reduced in size, and its connecting method.