The present invention is aimed at providing a method for simply measuring the liquid quantity of liquid material in a receptacle. A liquid quantity measuring apparatus for use in a liquid material supplying system comprising a receptacle for storing liquid material, a first pipe for feeding feeder gas into said receptacle, a first shutoff valve provided in said first pipe, a second shutoff valve provided in said first pipe downstream of said first shutoff valve and a second pipe for supplying the liquid material from said receptacle to supplier's destinations, and for measuring the liquid quantity of the liquid material in said receptacle, the measuring apparatus comprising: —a first pressure detection means for detecting the pressure of feeder gas in said pipe between said first shutoff valve and said second shutoff valve; —a second pressure detection means for detecting the pressure of gas in said receptacle; and —an arithmetic processing means for seeking by arithmetic calculation the liquid quantity of the liquid material in said receptacle on the basis of the detection results of said first pressure detection means and said second pressure detection means.