Abstract: An apparatus and method for managing inventory in an Internet based multistage logistics collaborative system are provided. The apparatus includes: an inventory management apparatus for managing sale and inventory information in real time, determining whether an automatic product supply to perform or not based on inventory in each distributor, and calculating a proper supply quantity according to the determination result; a supply order generator for transmitting the calculated proper supply quantity to each distributor, creating a supply order after a corresponding distributor confirms and modifies a reservation of receiving a corresponding product, and storing the created supply order; and a sale order generator for generating a sale order of a corresponding distributor when the product is automatically supplied to the corresponding distributor from a manufacturer based on the created supply order, and storing the generated sale order in the sale information storing unit.