Recently, thanks to advancing computing power and evolving image and sensor processing, SLAM (Simultaneous Localization and Mapping) is collecting much attention in broad areas. Inspired by the former research efforts on SLAM, we develop a real-time LiDAR-based indoor localization system in this paper. The system estimates the user's self-position by using LiDAR SLAM and Visual-Inertial Odometry (VIO) and visualizes the user's time-series positions on the building floor map (global map) by adopting a 2D-to-2D localization method. For the system validation, we designed and implemented the prototype handheld system and carried out the validation tests on one floor of our university building. The validation tests confirmed that the system achieves real-time indoor localization.