In this paper, we propose the delivery problem on trees and two algorithms for the problem. The delivery problem on trees is that of minimizing the object delivery time from one node to another node using n various speed robots. Our first algorithm generates an optimal solution with some restrictions in handover places. In this algorithm, we assume that the handover can be made at a vertex of given tree. We try to find the handover places and the robots participate in handover from the start node to the destination node. The second algorithm extends the first one to remove the restriction about the handover places. The second algorithm still generates an optimal solution. The time complexities of both algorithms are $O((n+m)^2)$ where n is the number of robots and m is the number of nodes.