When consumable part such as pressure-resistant cover (300) is installed on a chemical solution injector (100), consumption degree data is read from storage means such as an RFID chip of the consumable part and temporarily held. If the consumption degree updated according to the use of the consumable part exceeds the consumption criteria, a replacement preliminary warning is outputted and the updated consumption degree data is written in the consumption storage means (310) of the consumable part. Since the consumption degree of a consumable part installed on a mechanical device is automatically detected and a replacement preliminary warning is issue to the user at an adequate timing, continuous use of a totally consumed part, unnecessary replacement of a non-totally consumed part is prevented.