An image forming device including an optical sensor, an ultrasound sensor, and a conveyance guide. The optical sensor and the ultrasound sensor are disposed alongside a conveyance path of a sheet and are used to determine sheet type. The conveyance guide guides the sheet along the conveyance path. The conveyance guide is structured such that, on the conveyance path between the optical sensor and the ultrasound sensor, the sheet is in contact with the conveyance guide while a portion of the sheet is in a light irradiation range of the optical sensor and a different portion of the sheet is in an ultrasound irradiation range of the ultrasound sensor.