This paper describes a localization method for wearable computer users. To realize applications of wearable computers like a navigation system, the position of a user is required for location-based services. Many localization methods in indoor environments have been proposed. One of the methods estimates user's position using IR beacons or visual markers. However, these methods have same problems concerning power supply and/or undesirable visual effects. In order to avoid the problems, we propose a new localization method which is based on using an IR camera and invisible markers consisting of translucent retro-reflectors. In the proposed method, to extract the regions of the markers from the captured images stably, the camera captures the reflection of IR LEDs which are flashed on and off synchronously.