An electrostatic discharge protector including two electrodes for forming a discharge gap, and a discharge gap filling-member including a discharge gap filing composition filed in the discharge gap, the discharge gap filling composition contains metal particles (A) obtainable by metal particles with a hydrolyzed product of a metal alkoxide represented by the following formula (1) and a binder component (C), and the electrostatic discharge protector includes the composition; R—O-[M(OR)2—O—]n—R  (1) wherein M is a metal atom, O is an oxygen atom, R is an alkyl group, all or a part of R's may be the same as or different each other, and n is an integer of 1 to 40. Also disclosed is an electronic circuit board including the electrostatic discharge protector and an electronic device.