To provide an in-vivo indwelling device for embolization that suppresses changes in the dimensions of the coil portion (11) when sterilized, it has proximal and distal sides and extends the lumen in the longitudinal direction. The spring constant of the coil portion (11) is 1.0 N / mm in the indwelling tool for embolization having the coil portion (11) provided and the extension suppressing member (20) arranged in the lumen. The extension suppressing member (20) has a corrugated shape, and the wave height, which is the distance between the inner apex of the waveform of the extension suppressing member (20), is 35 μm or more and the coil portion (11). It was made smaller than the inner diameter.滅菌処理した際に、コイル部分（１１）の寸法の変化が抑えられる塞栓形成用体内留置具を提供するために、近位側および遠位側を有し、長軸方向に渡って管腔を備える前記コイル部分（１１）と、前記管腔内に配置される伸張抑制部材（２０）とを有する前記塞栓形成用体内留置具において、前記コイル部分（１１）のばね定数が１．０Ｎ／ｍｍ以下であり、前記伸張抑制部材（２０）は波形の形状を有し、前記伸張抑制部材（２０）の波形の内側の頂点間の距離である波高を、３５μｍ以上かつ前記コイル部分（１１）の内径より小さくした。
