An embodiment of the present disclosure relates to a detector that includes an AD and detects charged particles or light, and enables speeding up of response of the detector without changing a structure of the AD that limits the response of the detector. A drive circuit of the AD includes a first capacitor and a first resistor. Both the first capacitor and the first resistor are connected in series to the AD in a state where both terminals are set to have the same potential. This configuration reduces the apparent capacitance of the AD and speeds up the response of the entire detector including the drive circuit.