An evaporator includes an introducing portion that introduces a heat source gas from a heat source gas pipe, a heat source gas passage through which the heat source gas introduced from the introducing portion flows, a heating portion that is disposed in the heat source gas passage and at which a working fluid is heated by the heat source gas, an increasing portion at which a cross-sectional area of the heat source gas passage gradually increases from an upstream side towards a downstream side in the heat source gas passage, and a flow regulating plate that is disposed on an upstream side from the heating portion in the heat source gas passage and that has a plurality of holes which allow the heat source gas to pass through the plurality of holes.