To provide a reactor, an electricity generator, and an electronic apparatus each of which can easily cope with even the case when a carbon monoxide removal apparatus is overheated by cooling the removal apparatus.

The low-temperature reaction section 606 of a microreactor module 600 is provided with a combustion fuel feed passage 716 (reaction passage) in the inside of which reactants flow and react with each other, A fluid is allowed to pass through the combustion fuel passage 716, whereupon the passage 716 can serve also as a cooling passage for cooling the low-temperature reaction section 606.