Delivery of a good quality of service in an efficient manner requires matching the supply of capacity with customer demand. Much research has employed queueing models that analyzed the service system on the basis of independent and stationary customer arrivals. However, the appointment system, which is widely used to facilitate customer access to service in many industries including healthcare, has significant influence on the customer arrival process so that the independent and stationary assumption does not hold in an appointment-based service system. In this regard, this paper aims to propose a model for accurate illustration of the appointment-based customer arrival process. The use of the proposed model allows us to evaluate the overall system performance such as mean waiting time and service level under various appointment policies instead of conducting simulation studies.