It is difficult to identify whether quality requirements are defined adequately or not, but there are few methods to support this kind of requirements analysis. In this paper, we propose a method based on software quality spectrum, that shows a ratio of quality characteristics embedded in a software engineering artifact, such as a requirements specification, a manual and so on. We assume similar kinds of software systems have similar spectrum, thus we can identify the adequacy of quality requirements for a new system by using spectrum of already existing similar systems. We confirmed the assumption above by analyzing actual software systems, i.e., web browsers and drawing tools. Categories and Subject Descriptors D.2.1 [Software Engineering]: Requirements Specifications General Terms Requirements Analysis Keywords Quality Requirements, Non-functional Requirements