1. A switching apparatus for learning a source address set in a packet in an address learning table and delivering a packet on the basis of an address learned in said address learning table, said switching apparatus comprising: an address learning unit for limiting a number of learned addresses such that a number of learned addresses in said address learning table for each of user groups which are classified into a plurality of groups based on header information set in said packet is equal to or less than an address learning upper limit value for said user group; and a learning number counter for storing a number of learned addresses for each user group of said plurality of said user groups in said address learning table, wherein said address learning upper limit value is set for each user group, and said address learning unit limits the number of learned addresses of a user group judged based on a header information of a received packet in said plurality of user groups in said address learning table and updates the number of learned addresses of the user group in the learning number counter when the number of learned addresses for the user group does not exceed the address upper limit.