In order to provide a substrate for medical applications, which may be freely elastically deformed depending on a shape of a defective portion or hemostasis portion in a living body, is biocompatible and suitable for tissue regeneration or cell proliferation, or hemostasis, and can be easily manufactured. A collagen substrate of the present invention includes a three-dimensional mesh formed of spun collagen filaments. Preferably, the collagen substrate of the present invention includes cotton formed of spun collagen filaments.