The User requirements of many web-based services are dynamically and continuously changing even during the service time itself. For that reason, web service companies always keep trying to satisfy users' needs from the market. Requirements elicitation, among the processes in requirements engineering, is a process requiring high costs and time. Thus, a company planning to conduct the process wants to catch the points users don't satisfy in their needs by taking advantage of an effective process of requirements elicitation. In this paper, we propose value based requirements elicitation, so called, the Value Gap Model aiming to clarify need selection and focus on key factors to a requirements engineer who should take into account the value on behalf of users. To do that, the process, at first, recognizes a value gap between the value users currently have and the value a system understand as users' one, and then it figures out the components that a requirements engineer has to select and focus on in his or her requirements elicitation process. In order to focus on and invest effectively the resources of elicitation process, the proposed process finds the part where most of users feel unsatisfying so that it eventually elicits the valuable requirements from users.