An image forming apparatus includes an image forming unit for forming an image on a recording material, a first detection unit including a transmission unit for transmitting an ultrasonic wave and a reception unit for receiving the transmitted ultrasonic wave, first and second conveyance units for conveying the recording material, and a control unit. The first and second conveyance units form a loop on the recording material by conveying the recording material at different speeds. The control unit controls an image forming condition for forming an image on the recording material by the image forming unit, based on the ultrasonic wave received via the recording material in a period in which no loop is formed on the recording material by the first and second conveyance units.