An electronic device comprising: a casing provided with a first printed circuit board that includes a first connector; a unit inserted into the casing through a housing opening formed in the casing, the unit including a second printed circuit board with a second connector that connects to the first connector; a pair of guide rails (60, 70) that are provided inside the casing separated from each other and facing each other in a top-bottom direction, that slidably support the unit inserted through the housing opening and that guide the second connector towards the first connector; characterized by further comprising a width direction positioning section that is provided to an end portion on the housing opening side of at least one of the guide rails of the pair of guide rails (60, 70) and that positions the second connector in the unit in a width direction with respect to the first connector; and a top-bottom direction positioning section that is positioned further towards the first connector side than the width direction positioning section and that positions the second connector in the top-bottom direction with respect to the first connector, wherein the second printed circuit board is disposed with the board thickness direction oriented along the unit width direction; the unit includes an upper side slide portion jutting out to both board thickness direction sides of the second printed circuit board; the guide rail on the upper side includes an upper side guide groove portion that extends along the guide rail and slidably supports the upper side slide portion from both board thickness direction sides, and a pair of guide ribs that project out from each inside face (62B1) of the upper side guide groove portion towards each other and slidably support the upper side slide portion from below; and the top-bottom direction positioning section is configured by inclined faces that are formed to an upper face of the pair of guide ribs and are inclined downwards on progression towards the housing opening side. a casing provided with a first printed circuit board that includes a first connector; a unit inserted into the casing through a housing opening formed in the casing, the unit including a second printed circuit board with a second connector that connects to the first connector; a pair of guide rails (60, 70) that are provided inside the casing separated from each other and facing each other in a top-bottom direction, that slidably support the unit inserted through the housing opening and that guide the second connector towards the first connector; characterized by further comprising a width direction positioning section that is provided to an end portion on the housing opening side of at least one of the guide rails of the pair of guide rails (60, 70) and that positions the second connector in the unit in a width direction with respect to the first connector; and a top-bottom direction positioning section that is positioned further towards the first connector side than the width direction positioning section and that positions the second connector in the top-bottom direction with respect to the first connector, wherein the second printed circuit board is disposed with the board thickness direction oriented along the unit width direction; the unit includes an upper side slide portion jutting out to both board thickness direction sides of the second printed circuit board; the guide rail on the upper side includes an upper side guide groove portion that extends along the guide rail and slidably supports the upper side slide portion from both board thickness direction sides, and a pair of guide ribs that project out from each inside face (62B1) of the upper side guide groove portion towards each other and slidably support the upper side slide portion from below; and the top-bottom direction positioning section is configured by inclined faces that are formed to an upper face of the pair of guide ribs and are inclined downwards on progression towards the housing opening side.