Provided is an inexpensive image forming apparatus capable of monitoring the generating state of various powders. The image forming apparatus includes a minute-particle-measuring device, a toner-particles-detecting air duct, a paper-dust-detecting air duct, and blower fans. The minute-particle-measuring device detects the concentration of minute particles in air. The toner-particle-detecting air duct is an air duct leading from the image forming unit to the minute-particle-measuring device. The paper-dust-detecting air duct is an air duct leading from the paper-conveying path to the minute-particle-measuring device. The blower fans are respectively provided in the toner-particle-detecting air duct and the paper-dust-detecting air duct, and generate airflow that flows toward the minute-particle-measuring device side. The blower fans in the toner-particle-detecting air duct and in the paper-dust-detecting air duct are switched.