An adjuster device for adjusting the length and fastening of a web type strap, said device comprising: a base having a bottom frame extending in a first plane, said base defining at least one longitudinally elongated slot; an operating handle comprising a first pin extending along a first axis, said operating handle being pivotally arranged to the base about a pivot axis being parallel to said first plane, and said operating handle being movable between a release position and a fastening position; a second pin extending along a second axis being parallel to said pivot axis, said second pin being engaged in said slot and slidably movable therein between a first end position and a second end position; wherein a strap entrance is defined between said second pin and the bottom frame such that a strap, having a free first strap end outside of the strap entrance, is receivable through the strap entrance, characterized in that the strap passes thence around the first pin and thence through a strap exit arranged in an adjacent relation to said bottom frame to thereby provide a second strap end connectable to a child restraint harness; and wherein the device being configured such that when the operating handle is in its release position, the second pin is freely movable in said slot between the first end position and the second end position, and when the operating handle is in its fastening position, the second pin is squeezed to said first end position by parts of the strap brought into contact while still allowing the strap to be tightened by pulling the free first strap end in a first direction, whereas an increased tension on the second strap end causes a restraining action arising at least in part from friction between said parts of the strap. a base having a bottom frame extending in a first plane, said base defining at least one longitudinally elongated slot; an operating handle comprising a first pin extending along a first axis, said operating handle being pivotally arranged to the base about a pivot axis being parallel to said first plane, and said operating handle being movable between a release position and a fastening position; a second pin extending along a second axis being parallel to said pivot axis, said second pin being engaged in said slot and slidably movable therein between a first end position and a second end position; wherein a strap entrance is defined between said second pin and the bottom frame such that a strap, having a free first strap end outside of the strap entrance, is receivable through the strap entrance, characterized in that the strap passes thence around the first pin and thence through a strap exit arranged in an adjacent relation to said bottom frame to thereby provide a second strap end connectable to a child restraint harness; and wherein the device being configured such that when the operating handle is in its release position, the second pin is freely movable in said slot between the first end position and the second end position, and when the operating handle is in its fastening position, the second pin is squeezed to said first end position by parts of the strap brought into contact while still allowing the strap to be tightened by pulling the free first strap end in a first direction, whereas an increased tension on the second strap end causes a restraining action arising at least in part from friction between said parts of the strap.