A circuit board assembly comprising: a first circuit board having a first contact portion and a first opening portion (G1A, G1B, G1, 91A, 91B) ; a second circuit board having a second contact portion and a second opening portion (G2A, G2B, G2); and a connector for overlapping the first circuit board and the second circuit board in a connecting direction to electrically connect the first contact portion and the second contact portion to each other, wherein the connector includes: a flat plate portion ; and one or more guide pins protrudingly formed on a surface of the flat plate portion, wherein each of the one or more guide pins includes a first fitting portion (F1A, F1B, F1) disposed on a root side of the guide pin and fitted in the first opening portion (G1A, G1B, G1, 91A, 91B) of the first circuit board and a second fitting portion (F2A, F2B, F2) disposed on a tip side of the guide pin and fitted in the second opening portion (G2A, G2B, G2) of the second circuit board, and the first fitting portion has a size (S1A, S1B) larger than that of the second fitting portion in a direction perpendicular to the connecting direction, CHARACTERIZED IN THAT the size (S1A, S1B) of the first fitting portion (F1A, F1B, F1) is larger than that of the second opening portion (G2A, G2B, G2) in the direction perpendicular to the connecting direction. a first circuit board having a first contact portion and a first opening portion (G1A, G1B, G1, 91A, 91B) ; a second circuit board having a second contact portion and a second opening portion (G2A, G2B, G2); and a connector for overlapping the first circuit board and the second circuit board in a connecting direction to electrically connect the first contact portion and the second contact portion to each other, wherein the connector includes: a flat plate portion ; and one or more guide pins protrudingly formed on a surface of the flat plate portion, wherein each of the one or more guide pins includes a first fitting portion (F1A, F1B, F1) disposed on a root side of the guide pin and fitted in the first opening portion (G1A, G1B, G1, 91A, 91B) of the first circuit board and a second fitting portion (F2A, F2B, F2) disposed on a tip side of the guide pin and fitted in the second opening portion (G2A, G2B, G2) of the second circuit board, and the first fitting portion has a size (S1A, S1B) larger than that of the second fitting portion in a direction perpendicular to the connecting direction, CHARACTERIZED IN THAT the size (S1A, S1B) of the first fitting portion (F1A, F1B, F1) is larger than that of the second opening portion (G2A, G2B, G2) in the direction perpendicular to the connecting direction. a flat plate portion ; and one or more guide pins protrudingly formed on a surface of the flat plate portion, wherein each of the one or more guide pins includes a first fitting portion (F1A, F1B, F1) disposed on a root side of the guide pin and fitted in the first opening portion (G1A, G1B, G1, 91A, 91B) of the first circuit board and a second fitting portion (F2A, F2B, F2) disposed on a tip side of the guide pin and fitted in the second opening portion (G2A, G2B, G2) of the second circuit board, and the first fitting portion has a size (S1A, S1B) larger than that of the second fitting portion in a direction perpendicular to the connecting direction, CHARACTERIZED IN THAT the size (S1A, S1B) of the first fitting portion (F1A, F1B, F1) is larger than that of the second opening portion (G2A, G2B, G2) in the direction perpendicular to the connecting direction. <EOS>