Domain knowledge is one of crucial factors to get a great success in requirements elicitation of high quality, and only domain experts, not requirements analysts, have it. We propose a new requirements elicitation method ORE (Ontology based Requirements Elicitation), where a domain ontology can be used as domain knowledge. In our method, a domain ontology plays a role on semantic domain which gives meanings to requirements statements by using a semantic function. By using inference rules on the ontology and a quality metrics on the semantic function, an analyst can be navigated which requirements should be added for improving completeness of the current version of the requirements and/or which requirements should be deleted from the current version for keeping consistency. We define this process as a method and evaluate it by an experimental case study of software music players.