PURPOSE: To provide an automatic binding apparatus by placing a serrated plastic strap in parallel to the side section of the apparatus and furnishing the retaining arm of a hollow retainer with teeth which mates with the serrations of the strap.

CONSTITUTION: A plastic strap 52 comprises a rectangular continuous flexible band, one side of which is furnished with two parallel serrations 54 and 56. Flat edges 58 in a continuous form in a longitudinal direction are formed along the facing sides of the serrations 54, 56 to form a guide element in the transverse direction for a strap 52. The inside of a retainer 62 is furnished with two spring arms 70, 72 extending from the opening of flat surface 66 and having serrations 74 which are offset from each other so that they can mate with the serrations 54 and 56 of the strap 52 respectively. The strap 52 passes twice through the inside of the retainer 62 and is supported by a guide surface 78. The serrations 54 and 56 are faced outward and furnished with the serration 74 of the spring arms 70, 72, thereby enabling to bind the cable bundle.