A charge amplifier that converts a charge signal to a voltage signal includes: a first conductive member through which the charge signal propagates; a second conductive member that is provided along at least a portion of the first conductive member; an insulating member provided between the first conductive member and the second conductive member; a potential controlling voltage signal output circuit that is connected to the second conductive member, and is configured to supply a potential controlling voltage signal to the second conductive member; and an integrating circuit that includes an input terminal and an output terminal, the input terminal being connected to the first conductive member, and is configured to output the voltage signal from the output terminal.