1. A user interface apparatus for control of service robots, comprising: an interaction server for receiving a control command to control a service robot from a user, analyzing the control command, and outputting a result of the analysis to the user; an index block for determining a degree of difficulty of the analyzed control command; and a robot control server for determining an operating mode of the service robot depending on the analyzed control command and the degree of difficulty, and controlling the service robot in the determined operating mode, wherein the index block comprises a degree-of-difficulty determination module for determining the degree of difficulty of the control command, requested by the user, by applying service time and a service area, required for performance of the control command input from the user, to an artificial intelligence algorithm.