The present invention relates to a program executing 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 means and a command execution means. When the program interpreter sends a command in a program to the command rejection means, the command rejection means searches a command rejection rule storage section for a command rejection rule corresponding to the command, and if the rule is detected, retrieves 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 means when the conditions are not met.