The purpose of the present invention is to provide an agent for restoring a visual function or an agent for preventing the deterioration in a visual function, which has an excellent visual function restoring ability. The agent for regenerating a visual function or the agent for preventing the deterioration in a visual function according to the present invention contains, as an active ingredient, a chimeric protein having both an amino acid sequence for a microorganism-origin ion-transporting receptor rhodopsin and an amino acid sequence for an animal-origin G-protein-coupled receptor rhodopsin. The chimeric protein is preferably one in which an amino acid sequence for a cytoplasm-side second loop and/or a cytoplasm-side third loop in the amino acid sequence for the microorganism-origin ion-transporting receptor rhodopsin is substituted by an amino acid sequence for a cytoplasm-side second loop and/or a cytoplasm-side third loop in the G-protein-coupled receptor rhodopsin.