A gas sample introduction device includes a sample container connection flow path, a sample loop and a first flow path switching valve, having a first state in which the pressurizing gas is supplied to the sample container connection flow path via the sample loop and a second state in which the pressurizing gas is supplied to the sample container connection flow path without via the sample loop. A leak check method includes a first determination step of determining whether or not there is a gas leak by setting the first flow path switching valve to a first state and a second determination step of identifying a location of a gas leak by performing a second determination of whether or not there is a gas leak by setting the first flow path switching valve to a second state, when there is a gas leak in the first determination step.