PROBLEM TO BE SOLVED: To provide a means for clarifying a function after the birth (particularly an imago) of an Ror2 (receptor tyrosine kinase-like orphan receptor 2).SOLUTION: A non-human mammal homogeneously has an Ror2 gene structured to hold at least one exon by a plurality of loxP sequences, wherein at least one of the plurality of loxP sequences is present in a non-translated region or an intron of the Ror2 gene, and Cre protein is expressed in at least a part of the body.