A method, system and program processing unit for a robot, by which the safety during execution of a program is improved. The program processing unit comprises a program interpreter, a command rejection device and a command execution device. When the program interpreter sends a command in a program to the command rejection device, the command rejection device searches a command rejection rule storage section for a command rejection rule corresponding to the command, and if the rule is detected, retlieves input values from one or more sensors and the source information of the program from a source information storage section, judges command rejection conditions included in the rule based on the sensor information, source information, the command and its parameters, dismisses the command when the conditions are met, and sends the command to the command execution device when the conditions are not met.