The present invention provides a stretchable fastener stringer for a slide fastener in which an element row is attached to a stretchable fastener tape, the slide fastener being capable of preventing occurrence of chain breaking even when coupled element rows receive pushing force and capable of stably maintaining a coupled state of the element rows. The stretchable fastener stringer according to the present invention includes a fastener tape (2) having a tape main portion (2a) and an element attaching portion (2b) and a continuous fastener element (3) which is attached to the element attaching portion (2b). The fastener tape (2) has stretchability due to an elastic yarn (8) being combined by weaving or knitting and the fastener element (3) includes a coupling head (3a), upper and lower leg portions (3b, 3c) which are extended from the coupling head (3a) and a connecting portion (3d) which connects the upper and lower leg portions (3b, 3c) therebetween of adjacent fastener elements (3). In this fastener stringer (1), a value of a bulging ratio (= mountain length H / leg portion length d) which is the ratio between a dimension of the coupling head (3a) in the tape longitudinal direction (= mountain length H) and a dimension of the upper and lower leg portions (3b, 3c) in the tape longitudinal direction (= leg portion length d) is set to be larger than 1.80 and not larger than 2.33.