1. An apparatus for disposing of fuel-vapor comprising: a charcoal canister for absorbing the fuel-vapor evaporating from a fuel tank of an engine; a purge valve arranged in a purge pipe which connects said charcoal canister and an inlet pipe, and controls the flow rate of the purge gas; an air-fuel ratio detecting means arranged in an exhaust pipe of the engine for detecting the air-fuel ratio of the exhaust gas; an air-fuel ratio control means for calculating an air-fuel ratio correction factor in order to control the air-fuel ratio detected by said air-fuel ratio detecting means to a predetermined target air-fuel ratio; a vapor concentration learning means for learning the vapor concentration of the fuel-vapor purged into the inlet pipe in accordance with the air-fuel ratio correction factor calculated by said air-fuel ratio control means; a basic air-fuel ratio correction factor learning means for learning the base air-fuel ratio correction factor in accordance with the air-fuel ratio correction factor calculated by said air-fuel ratio control means; and a purge valve control means for controlling the opening of the purge valve in accordance with the air-fuel ratio correction factor calculated by said air-fuel ratio control means, the vapor concentration learned by said vapor concentration learning means and the basic air-fuel ratio correction factor learned by said basic air-fuel ratio correction factor learning means; wherein said apparatus for disposing of fuel-vapor further includes a learning control means, which opens said purge valve, allows the learning of the concentration of the fuel-vapor by said vapor concentration learning means, and inhibits the learning of the basic air-fuel correction factor by said basic air-fuel correction factor learning means when it is determined that the basic air-fuel correction factor has been learned by said basic air-fuel correction factor learning means, or when it is determined that the basic air-fuel correction factor has not been learned by said basic air-fuel correction factor learning means and the concentration of fuel-vapor in the purged gas is high, and which closes said purge valve, inhibits the learning of the concentration of the fuel-vapor by said vapor concentration learning means, and allows the learning of the basic air-fuel correction factor by said basic air-fuel correction factor learning means when it is determined that the basic air-fuel correction factor has not been learned by said basic air-fuel correction factor learning means and the concentration of fuel-vapor in the purge-gas is low.