A pump apparatus is capable of suppressing an unintentional ejection of a high pressure liquid from a nozzle, the pump apparatus including: an injection chamber (31) having a door (33); a nozzle (27) arranged in the injection chamber (31); a pump (13) connected to the nozzle (27) for discharging liquid; a motor (16) for driving the pump (13); a door sensor (34) for detecting that the door (33) is closed; and a control device (51) capable of communicating with the door sensor (34), the control device (51) having a motor rotation unit (52b) for supplying driving power to the motor (16) only when the door sensor (34) detects that the door (33) is closed. A method of operating the pump apparatus is also disclosed.