A scroll expander includes: a driving scroll body having a first axis line as a rotary shaft line; a driven scroll body having, as a rotary shaft, a second axis line shifted with respect to the first axis line; a bearing plate having the second axis line as a rotary shaft; a cylindrical driving pin attached to the driving scroll body; and a cylindrical guide ring attached to the bearing plate and having an inner diameter larger than an outer diameter of the driving pin. Four driving pins are disposed on the circumference of a circle around the first axis line at an equal interval. Four guide rings are disposed on the circumference of a circle around the second axis line at the equal interval so as to correspond to the four driving pins.