PROTECTION DEVICE

In a protection device of a current amplifier circuit, to protect the current amplifier circuit against more high-speed operation than recovery time of a relay device and to protect operation of the current amplifier circuit in a wide range from low frequency side to high frequency side. A protection device (30) includes a detection circuit (32) that detects an abnormal current value of a current amplifier circuit (14) and outputs a first abnormality detection signal. The protection device (30) outputs a second abnormality detection signal continuously for predetermined time that starts from output timing of the first abnormality detection signal, turns down an input voltage value to the current amplifier circuit (14) at receiving timing of the second abnormality detection signal, and outputs a cutting command signal to a relay device (36) at the same timing. The detection circuit (32) includes a load line detection unit (42) that detects abnormality by a current value on a load line and a pulse response characteristic changing unit (44) changes frequency characteristic of abnormality detection operation by the load line detection unit (42).