Provided are a photodegradable hydrogel in which cells can be embedded in the photodegradable gel without causing cytotoxicity when the cells are embedded in the photodegradable gel by allowing the cells to coexist at the time of preparation of the photodegradable gel, and which contains a protein as one of the main components; a culture device using the same; a method for forming tissue; and a method for separating cells. A photodegradable hydrogel is obtained by condensation of an alkyne group contained in a cyclooctyne ring or an azacyclooctyne ring of the following compound A with an azido group of the following compound B. (Compound A) A compound is a photocleavable crosslinker which contains a main chain having a linear type- or a branched type- (of three or more branches) polyethylene glycol structure, a photodegradable nitrobenzyl group disposed at both terminals or a branched terminal of the main chain, and a group having a cyclooctyne ring or an azacyclooctyne ring disposed at a terminal side of the nitrobenzyl group. (Compound B) A compound is an azide-modified protein in which a main chain is a protein and at least some of an amino group present at lysine and arginine side chains of the main chain and an amino group present at a terminal of the main chain are modified with the azido group.