Travel-lane estimation system

A travel-lane estimation system includes: a GNSS receiver; a vehicle-speed calculator; an angular-velocity measurement mechanism; a subject-vehicle-position positioner calculating a vehicle's reference coordinate and reference orientation from a GNSS coordinate, and calculating time series data of vehicle's positions; a map information storage storing positional information about a division line of each lane; and a lane estimator calculating, as an optimal correction amount, an error pattern having a highest posterior probability among plural error patterns, correcting the time series data using the optimal correction amount, and comparing the corrected time series data with the division line, to estimate a vehicle's travel lane, the posterior probability calculated with the product of prior occurrence probability of the time series data by the plural error patterns and a likelihood calculated, under condition that the error pattern has occurred, based on a relative positional relationship between the corrected time series data and the division line.