The design of a laser fusion reactor with a dry wall chamber has been carried out. According to a simple point model calculation, sufficient pellet gain (G > 100) can be achieved with the injection energy of 400kJ under relatively conservative parameters ( = 2, c = 0.05, h = 0.2). Assuming the pulse heat load limit of a dry wall to be 2J/cm2, chamber radius of R = 5.64m is achievable. 1-D thermal analysis also supports the feasibility of this design. Then a medium scale plant (400MWe electric output) can be designed with moderate construction cost, which suits for the first-step reactor, if the laser repetition rate can be increased to 30 Hz. Since laser fusion reactors have flexibility in changing its output, this design enables them to be in flexible use according to the time-varying electric demand as the present fossil fuel power plants. This design is remarkable because it gives a new property to the fusion reactors.