A fullness detection device comprising: a waste toner collecting portion (4, 42, 43, 45) configured to collect waste toner; a waste toner container configured to store the waste toner collected by the waste toner collecting portion (4, 42, 43, 45), the waste toner container transmitting light; a detecting portion including a light emitting portion and a light receiving portion disposed to sandwich the waste toner container, the light emitting portion emitting light to the light receiving portion when a predetermined timing of performing fullness detection of the waste toner container comes, the light receiving portion receiving the light from the light emitting portion so as to output different values depending on received light intensity; a determining portion configured to determine whether or not the waste toner container is full based on whether or not output value of the light receiving portion is higher than a predetermined threshold value; and a light emission controller configured to increase light intensity of the light emitting portion step by step in the fullness detection and for controlling the light emitting portion to emit light at a level of smallest light intensity among light intensity levels at which the determining portion can determine that the waste toner container is not full, characterized by a storage portion configured to store the level at which it was determined that the waste toner container was not full in the last fullness detection, wherein the light emitting portion starts light emission at light intensity of the level stored in the storage portion when the timing of performing the fullness detection of the waste toner container comes, and on detecting fullness of the waste toner container, the determining portion controls the storage portion to store data for controlling the light emitting portion to emit light at the minimum light intensity, and resets the light intensity of the light emitting portion to be minimum. a waste toner collecting portion (4, 42, 43, 45) configured to collect waste toner; a waste toner container configured to store the waste toner collected by the waste toner collecting portion (4, 42, 43, 45), the waste toner container transmitting light; a detecting portion including a light emitting portion and a light receiving portion disposed to sandwich the waste toner container, the light emitting portion emitting light to the light receiving portion when a predetermined timing of performing fullness detection of the waste toner container comes, the light receiving portion receiving the light from the light emitting portion so as to output different values depending on received light intensity; a determining portion configured to determine whether or not the waste toner container is full based on whether or not output value of the light receiving portion is higher than a predetermined threshold value; and a light emission controller configured to increase light intensity of the light emitting portion step by step in the fullness detection and for controlling the light emitting portion to emit light at a level of smallest light intensity among light intensity levels at which the determining portion can determine that the waste toner container is not full, characterized by a storage portion configured to store the level at which it was determined that the waste toner container was not full in the last fullness detection, wherein the light emitting portion starts light emission at light intensity of the level stored in the storage portion when the timing of performing the fullness detection of the waste toner container comes, and on detecting fullness of the waste toner container, the determining portion controls the storage portion to store data for controlling the light emitting portion to emit light at the minimum light intensity, and resets the light intensity of the light emitting portion to be minimum.