A sheet conveying device includes a conveying path along which a sheet is conveyed. First and second conveying roller pairs are arranged on the conveying path at a predetermined distance from each other. Overlapping conveyance sensing devices are located between the first and second conveying roller pairs and include opposing transmission device and reception device. A distance between the first and second conveying roller pairs is shorter than a length of a minimum size sheet in a conveying direction. In the conveying path between the conveying roller pairs, guide members are disposed to sandwich the transmission device and reception device. The guide members are configured to project upward or downward from a sheet conveying line by a predetermined amount with respect to the conveying path, the sheet conveying line extending through nip points of the first and second conveying roller pairs.