1. An image encoding device, comprising: a memory that stores instructions, and a processor that executes the instructions, wherein, when executed by the processor, the instructions cause the device to perform operations including: initializing an image quality control parameter and calculating an update of the image quality control parameter based on a degree of importance of a past time corresponding to a current time in a degree of importance period, which is a period of a degree of importance of a plurality of input images which are consecutively input; encoding the input images using the image quality control parameter and generating video data; and calculating a complexity of the video data generated by the image encoder, wherein the updated image quality control parameter is calculated based on the complexity.