An image forming apparatus includes a fixing unit fixing a toner image onto a sheet. The at least one heating means is energized to heat at least when the at least one thin-film magnetic head element operates. Additionally, the power system may include a motorgenerator drivingly connected to at least one of the prime mover and the transmission. The second case is attached to a top face of the first case. Another possible deviation indicative for the occurrence of a flash is a substantial decrease of the storage time of the line deflection transistor.