Recording medium determination apparatus and image forming apparatus

An image forming apparatus, comprising:

• an image forming unit configured to form an image on a recording medium;
• a transmission unit configured to transmit an ultrasonic wave;
• a receiving unit configured to receive an ultrasonic wave transmitted from the transmission unit via the recording medium and output a first signal corresponding to the received ultrasonic wave, and to receive an ultrasonic wave transmitted from the transmission unit not via the recording medium and output a second signal corresponding to the received ultrasonic wave;
• a detection unit configured to detect a value of the first signal and a value of the second signal output from the receiving unit;
• a control unit configured to control an image forming condition of the image forming unit based on the value of the first signal detected by the detection unit;
• and
• a measurement unit configured to measure a period of time from when the transmission unit transmits the ultrasonic wave to when the detection unit detects the value of the second signal,
• wherein the control unit is configured to calculate, based on a period of time measured by the measurement unit in a first condition and a period of time measured by the measurement unit in a second condition that is different from the first condition, variation of a distance between the transmission unit and the receiving unit from the first condition to the second condition, to thereby control the image forming condition of the image forming unit in accordance with the calculated variation of the distance and the value of the first signal.