To provide a leaked gas detector that can stably and appropriately evaluate and judge the amount of leaked gas and can efficiently inspect works whose shape and size differ.

The leaked gas detector 10 comprises a chamber 11 for retaining a body W to be inspected, where the opening is subjected to sealing treatment, in the inside; a tracer gas supply section 12 that is placed on a base 11a in the sealed space of the chamber 11, whose tip is connected to a tracer gas introduction section A of the body W to be inspected, and supplies tracer gas to the body W to be inspected; a gas circulation section 13 for circulating gas around the body W to be inspected via a gas suction opening 11b and a gas discharge opening 11c provided at the chamber 11; and a gas detection section 14 for measuring the concentration of the tracer gas in circulation gas.