Hydrogen generation apparatus, operation method thereof, and fuel cell system

This hydrogen generation apparatus includes a feedstock supplier, a hydro-desulfurizer, a feedstock supply channel, a reformer, a hydrogen-containing gas flow channel, a recycle gas flow channel, an ejector, an on-off valve, and an abnormality detector. The abnormality detector has a pressure detector and a control unit. The control unit performs at least one control task among the control tasks of determining an abnormality, reporting the state of the hydrogen generation apparatus or the abnormality thereof, or stopping the operation, when the feedstock supplier is performing a supplying operation and the pressure value detected by the pressure detector with the on-off value open is lower than a first threshold or when the feedstock supplier is performing a supplying operation and the pressure value detected by the pressure detector after the on-off value has been closed from an open state does not fall below a second threshold that is set lower than the first threshold.