"An Arduino compatible for minimalists." We have designed a world standard prototyping tool that is essential for modern electronic work called Arduino, at the world's smallest size. Arduino contains a microcomputer, and is used for prototypes and development by engineers, designers and media artists, but conventional products were too big to integrate into their work efficiently. We provide enough "margin" resulting from the world's smallest size by eliminating all unnecessary space for users who pursue minimal work and product development. The material for users to smoothly develop has been realized without any compromise in usability when writing via the world's smallest original micro USB connecter.