A stretchable fastener stringer for a slide fastener includes a fastener tape having a tape main portion and an element attaching portion and a continuous fastener element which is attached to the element attaching portion. The fastener tape has stretchability due to an elastic yarn being combined by weaving or knitting and the fastener element includes a coupling head, upper and lower leg portions which are extended from the coupling head and a connecting portion which connects the upper and lower leg portions, therebetween of adjacent fastener elements. In this fastener stringer, a value of a bulging ratio which is the ratio between a dimension of the coupling head in the tape longitudinal direction and a dimension of the upper and lower leg portions in the tape longitudinal direction is set to be larger than 1.80 and not larger than 2.33.