An excavator configured to drive an electric work element using electric power from an electrical energy storage unit comprising: an arm including an attachment; a boom to which the arm is attached; an upper turning body to which the boom is attached; an engine arranged at the upper turning body; an electrical energy storage unit including an electrical energy storage device that accumulates electric power generated by a generator and an electric circuit that controls a charge/discharge operation of the electrical energy storage device; a voltage detection part that is arranged between the electrical energy storage device and the generator and is configured to measure a voltage of the electrical energy storage device; a current detection part that measures a current flowing through the electrical energy storage device; and an abnormality detection part that detects an abnormality of the electrical energy storage unit; a switching element (102A, 102B) that controls the charge/discharge operation of the electrical energy storage device; and a breaker that interrupts a power supply line between the switching element and the electrical energy storage device; wherein the abnormality detection part includes an electrical energy storage state estimation part that obtains an estimation value of an electrical energy storage state of the electrical energy storage device based on a voltage detection value obtained by the voltage detection part and a current detection value obtained by the current detection part; and an abnormality determination part that makes an abnormality determination based on the estimation value obtained by the electrical energy storage state estimation part; wherein the abnormality detection part controls the switching element and the breaker based on an abnormality determination result of the abnormality determination part; and wherein when a ratio of an amount of change (SOC2-SOC0) in a charge state of the electrical energy storage device to the corresponding estimated value (ΔSOC) is less than a first threshold value (F, S10), the abnormality determination part stops operation of the switching and controls the breaker to interrupt the power supply line. an arm including an attachment; a boom to which the arm is attached; an upper turning body to which the boom is attached; an engine arranged at the upper turning body; an electrical energy storage unit including an electrical energy storage device that accumulates electric power generated by a generator and an electric circuit that controls a charge/discharge operation of the electrical energy storage device; a voltage detection part that is arranged between the electrical energy storage device and the generator and is configured to measure a voltage of the electrical energy storage device; a current detection part that measures a current flowing through the electrical energy storage device; and an abnormality detection part that detects an abnormality of the electrical energy storage unit; a switching element (102A, 102B) that controls the charge/discharge operation of the electrical energy storage device; and a breaker that interrupts a power supply line between the switching element and the electrical energy storage device; a switching element (102A, 102B) that controls the charge/discharge operation of the electrical energy storage device; and a breaker that interrupts a power supply line between the switching element and the electrical energy storage device; wherein the abnormality detection part includes an electrical energy storage state estimation part that obtains an estimation value of an electrical energy storage state of the electrical energy storage device based on a voltage detection value obtained by the voltage detection part and a current detection value obtained by the current detection part; and an abnormality determination part that makes an abnormality determination based on the estimation value obtained by the electrical energy storage state estimation part; wherein the abnormality detection part controls the switching element and the breaker based on an abnormality determination result of the abnormality determination part; and wherein when a ratio of an amount of change (SOC2-SOC0) in a charge state of the electrical energy storage device to the corresponding estimated value (ΔSOC) is less than a first threshold value (F, S10), the abnormality determination part stops operation of the switching and controls the breaker to interrupt the power supply line.