Embracing uncertainty in software development is one of the crucial research topics in software engineering. In most projects, we have to deal with uncertain concerns by using informal ways such as documents, mailing lists, or issue tracking systems. This task is tedious and error-prone. Especially, uncertainty in programming is one of the challenging issues to be tackled, because it is difficult to verify the correctness of a program when there are uncertain user requirements, unfixed design choices, and alternative algorithms. This paper proposes iArch-U/MC, an uncertainty-aware model checker for verifying whether or not some important properties are guaranteed even if Known Unknowns remain in a program. Our tool is based on LTSA (Labelled Transition System Analyzer) and is implemented as an Eclipse plug-in.