1. A monitoring apparatus which generates and outputs an output moving image obtained by changing an image area of a person detected from an imaged moving image of a monitoring area to a mask image, the apparatus comprising: a processor; and a memory which stores instructions, wherein the monitoring apparatus further includes, as a configuration when the processor executes the instructions stored in the memory, a person image analyzer including a person detector which detects a person from the imaged moving image and acquires area information regarding each person and an attribute determinator which determines attributes for each person detected from the imaged moving image, a mask image setter which sets the mask image by the attribute, and a moving image output controller which generates and outputs the output moving image obtained by changing the image area for each person to the mask image by the attribute, based on the area information and the attribute for each person output from the person image analyzer.