To provide a boiler capable of using solid fossil fuel extremely difficult to ignite and including a low carbon content as fuel and an electric power generating device using the boiler.

The boiler includes: a housing 16 including a piping storage space 22b and a fuel storage space 22a vertically juxtaposed inside in this order and having a bottomed cylindrical shape and an opened upper part; a condensing lens 20 arranged above the housing 16, collecting sunlight and irradiating the sunlight from the upper opening of the housing 16 toward the solid fossil fuel F including a low carbon content and stored within the fuel storage space 22a; and steam piping 18 for steam discharge stored in the piping storage space 22b and having both side ends protruded outwardly from the housing 16.