WRITING UNIT FOR LED

PROBLEM TO BE SOLVED: To form a high quality image by transferring a driving data to a drive means based on the emission quantity detected through each of a plurality of LED elements and controlling the emission quantity each of the plurality of LED elements thereby correcting fluctuation in the emission of the LED elements. SOLUTION: First dot of an LED array 523 is lighted at the time of warming up a fixing heater and the quantity of light is read out by means of a photodiode 704 in a sensor unit 605 before delivering a quantity of light detection signal. The value thus read out is compared with a reference value and a signal for correcting the difference is stored in an RAM. Subsequently, the quantity of light of all LED elements is measured for 1 through 14336 dots and a correction signal is produced. An image data transferred to an LED head is further transferred to the 1 through 14336 dot positions of each element in the LED array 523 which is lighted only during the time of the emission quantity signal and the correction signal thereof and a latent image is formed on a photosensitive body drum.