In a high speed multicast route searching method of searching information of a transmission port to which a received multicast packet is next transferred: a route address is formed by coupling a receiver address and a sender address in this order; one p-th power-of-2-branch tree node is configured by a collection of one two-branch tree node and two-branch tree nodes of p−1 stages totalling ((p-th power of 2)−1) nodes just under the one two-branch tree node to form a p-th power-of-2-branch tree which is stored in a memory; not one bit but consecutive p bits of the route address coupling the receiver address and sender address in a received multicast packet in this order are checked at the same time; and in accordance with the values of the consecutive bits, a search tree stored in the memory is searched. In this manner, a search process can be completed by tracing nodes (the number of bits of a search key divided by p) times at a maximum, independently from the number of entries.