There is provided an opener of a slide fastener. A separable pin accommodation part of a retainer has upper and lower walls facing each other, a pair of wall parts protruding from the upper and lower walls in a direction of narrowing an interval therebetween, and a bottom wall configured to join the upper and lower walls at the rear of the pair of wall parts. The pair of wall parts extend toward the bottom wall from a rear side relative to front ends of the upper and lower walls. A pair of restriction parts are configured to collide with each other so as to restrict a position of a rearmost end of a separable pin to be inserted into a separable pin hole to a position between the bottom wall and front ends of the pair of wall parts are separately provided for the retainer and the separable pin.