A robot simulator comprising: a model storage module configured to store model information related to a robot and an obstacle (32, 33, 34) in the vicinity of the robot; an information acquisition module configured to obtain first input information defining a start position and an end position of operation of the robot; an information processing module configured to execute generation of a path for moving a distal end portion of the robot from the start position to the end position while avoiding a collision between the robot and the obstacle (32, 33, 34) based on the first input information and the model information and execute generation of image data including an illustration of the obstacle (32, 33, 34); and an image data output module configured to output the image data to a monitor, characterized in that the image data further includes an index indicating a via-point of the path and a line indicating the path, the information acquisition module is configured to, after the image data is output, further obtain second input information from a user for changing the position of the via-point, the information processing module is configured to execute regeneration of the path so as to pass through the via-point after a position change based on the second input information and further execute generation of image data in which the position of the index and the line indicating the path have been changed based on the second input information, the image data output module is further configured to output the image data in which the position of the index and the line indicating the path have been changed to the monitor, the information acquisition module is configured to further obtain further input information defining an accessible distance to the robot, and the information processing module is configured to further execute generation of an outer shell model covering the robot such that a minimum value of an interval between a model of the robot and the outer shell model is equal to or more than the accessible distance defined based on the further input information and generate the path for moving the distal end portion from the start position to the end position while avoiding a collision between the outer shell model and the obstacle (32, 33, 34) in generation of the path. a model storage module configured to store model information related to a robot and an obstacle (32, 33, 34) in the vicinity of the robot; an information acquisition module configured to obtain first input information defining a start position and an end position of operation of the robot; an information processing module configured to execute generation of a path for moving a distal end portion of the robot from the start position to the end position while avoiding a collision between the robot and the obstacle (32, 33, 34) based on the first input information and the model information and execute generation of image data including an illustration of the obstacle (32, 33, 34); and an image data output module configured to output the image data to a monitor, characterized in that the image data further includes an index indicating a via-point of the path and a line indicating the path, the information acquisition module is configured to, after the image data is output, further obtain second input information from a user for changing the position of the via-point, the information processing module is configured to execute regeneration of the path so as to pass through the via-point after a position change based on the second input information and further execute generation of image data in which the position of the index and the line indicating the path have been changed based on the second input information, the image data output module is further configured to output the image data in which the position of the index and the line indicating the path have been changed to the monitor, the information acquisition module is configured to further obtain further input information defining an accessible distance to the robot, and the information processing module is configured to further execute generation of an outer shell model covering the robot such that a minimum value of an interval between a model of the robot and the outer shell model is equal to or more than the accessible distance defined based on the further input information and generate the path for moving the distal end portion from the start position to the end position while avoiding a collision between the outer shell model and the obstacle (32, 33, 34) in generation of the path.