This paper presents a practical algorithm for topological navigation in corridor environment using cheap sonar sensors. Topological navigation consists of topological mapping and obstacle avoidance navigation. In this environment, it has two major problems which are 1) identifying nodes under globally similar but locally slightly different shape of corridor environment for topological mapping and 2) obstacle avoidance navigation using cheap sensors. In order to detect nodes robustly, we define the Eigenvalue Ratio (EVR) which converts geometrical shape of the environment to a quantitative value based on the Principal Component Analysis (PCA). This method is demonstrated by simulation and experiments to be robust, with the notable detail that at a given corridor intersection the method can detect a cluster of nodes defined in this manner. For safe obstacle avoidance navigation, we introduce Circle Following (CF) algorithm which uses geometry of environment and characteristics of sonar sensors. Experiments and simulation validate reliability of the CF algorithm.