A semantic word network is a network that represents the semantic relations between individual words or their lexical senses. In this paper, we present a software system for automatic construction of a semantic wordnetwork. The system, called SWN, is designed for the construction for such a semantic word network and includesthe implementation of unsupervised concept discovery and semantic relation establishing methods as well as theimplementation of a supervised relation expansion method. The methods use widely available language resources,such as semantic relation dictionaries and background text corpora. The domain model has been presented usingthe VOWL notation. The system architecture is represented using the UML notation and is composed of theconcept discovery module, semantic relation construction module, the Semantic Web export module, and theevaluation dataset construction module based on microtask-based crowdsourcing. The present software system isopen source and is available for integration into third-party data mining systems.