A fault diagnosis section activates a driving component alone, measures an operation state signal and a paper passage time, and stores feature values (Vm, .sigma.v, Tqs, .sigma.ts) extracted as a determination reference in a storage medium. A paper passage fault determination section determines whether or not a fault has arisen on the basis of the paper passage time when an apparatus is under normal operating conditions. A diagnosis target block determination section determines an order to operate a detail fault diagnosis when it is determined that there is a plurality of diagnosis target blocks. When the driving component is activated alone under actual operation conditions, the operation state signal Vf is obtained, and an operation state fault determination section conducts diagnosis on whether or not a fault has arisen on the driving component and a state of the fault, and whether or not a fault has arisen on other power transmission components and a nature of the fault with reference to the feature values as the determination reference on the basis of a degree of deviation from a normal range.