A connection structure includes: a circuit body including a flexible printed circuit having a wiring pattern; and a conductive body connected to a mounting surface of the circuit body using a solder. The conductive body has a pair of connection portions opposed to each other and extending along the mounting surface. The solder forms solder fillets located around the pair of connection portions and extending along the mounting surface. A first fillet width of one solder fillet among the solder fillets located in an inside region between the pair of connection portions is larger than a second fillet width of another solder among the solder fillets located in an outside region of one of the pair of connection portions, which is on a side opposite to the inside region across the one of the pair of connection portions.