  We develop a model for describing excited mesons decay into three mesons. The
properties of the excited mesons can be extracted with this model. The model
maintains the three-body unitarity that has been missed in previous data
analyses based on the conventional isobar models. We study an importance of the
three-body unitarity in extracting hadron properties from data. For this
purpose, we use the unitary and isobar models to analyze the same pseudo data
of gamma p -> pi+pi+pi-n, and extract the properties of excited mesons. We find
a significant difference between the unitary and isobar models in the extracted
properties of excited mesons, such as the mass, width and coupling strength to
decay channels.
