In the radiation detector, a capacitor is connected between a connecting wire which is connected with a preamplifier (amplifier) and another connecting wire. Specifically, the capacitor is connected between the connecting wire and another connecting wire which has the lowest electric resistance with respect to a signal wire among connecting wires connected with a radiation detecting element. This prevents electric current produced by static electricity from flowing to the signal wire and prevents the signal wire or the preamplifier from being damaged by static electricity. A circuit element for a countermeasure against static electricity is not provided at the signal wire, and therefore input capacitance of the preamplifier is kept low. Accordingly, the radiation detector is improved by a sufficient countermeasure against static electricity while input capacitance of the preamplifier is kept low.