PROBLEM TO BE SOLVED: Even if the diameter of a collar once becomes smaller (the collar is tightened) due to the movement of a pet wearing a collar, the diameter easily returns to its original size, and the pet keeps feeling cramped. Providing a pet animal collar to prevent it. SOLUTION: An annular collar body portion 2 to be attached to the neck of a pet animal, a lead connecting portion 4 connected to a lead, and a peripheral length of the collar body portion 2 connected to the lead connecting portion 4 are changed. And a length adjusting portion 6 for shortening the length of the circumference of the collar body portion 2 when the pulling force is applied to the lead, and the pulling force is released. In this case, the circumference of the collar body 2 is restored. [Selection diagram] Figure 1【課題】首輪を着用した愛玩動物の動作に伴い、一旦首輪の径が小さくなって（首輪が締まって）も、その径が元の大きさに戻り易く、愛玩動物に窮屈な思いをさせ続けないようにする愛玩動物用首輪を提供する。【解決手段】愛玩動物の首に装着する環状の首輪本体部２と、リードと接続されるリード接続部４と、リード接続部４に接続され、前記首輪本体部２の周囲の長さを変える長さ調整部６と、を有し、前記長さ調整部６が、前記リードに引く力が加えられた場合、前記首輪本体部２の周囲の長さを短くし、前記引く力が解除された場合、前記首輪本体部２の周囲の長さを復帰させることを特徴とする。【選択図】図１
