A method for connecting substrates is provided. The method includes the steps of: preparing a first wiring substrate having a first substrate including a first region and a second region which are provided with a first metal wire, wherein an area ratio between the first region and the first metal wires in the first region is different from an area ratio between the second region and the first metal wire in the second region; heating the first wiring substrate to bend the first wiring substrate; and electrically connecting a third wiring on a third substrate to the first metal wire provided on the first wiring substrate, thereby mounting the first wiring substrate on the third substrate in a manner that the first surface of the first substrate is nonparallel to the first surface of the third substrate.