In order to attain an object to realize an ion beam capable of (i) immediately determining energy of the ion beam to be generated, and (ii) measuring an ion beam in real time while carrying out laser irradiation, an ion beam detector (1) of the present invention includes a light conversion section (7) transmitting X-rays mixed in with ions (3) and converting the ions (3) to light; a light detection section (9) detecting, as an electric signal, the light converted from the ions (3) by the light converting section (7); a time-of-flight measurement section (10) measuring a time of flight for the ions (3) to reach the light conversion section (7); an electron removal section (5) removing electrons mixed in with the ions (3) and a light shielding section (6) shielding light mixed in with the ions (3), each of which is provided in an upstream of the light conversion section from which the ion beam comes to the light conversion section; and a curved section (8) between the light conversion section (7) and the light detection section (9), curved with respect to an optical axis of the ions (3) incident on the light conversion section (7).