An image forming apparatus capable of controlling an image forming position with high accuracy. The image forming apparatus has a plurality of image forming sections each including a photosensitive drum and a laser scanner. The laser scanner exposes the photosensitive drum to form an electrostatic latent image thereon. The image forming section develops the electrostatic latent image formed on the photosensitive drum to form a toner image, and the toner image is transferred onto an intermediate transfer belt. A thermistor in the laser scanner detects the internal temperature of the laser scanner. The image forming apparatus controls the image forming sections to form detection patterns on the intermediate transfer belt. An image forming position is corrected based on the temperature detected by the thermistor and a result of measurement of the detection patterns.