Disclosed is light-driven actuator element characterized in that, inter alia, it can be reduced to micrometer size, is rapidly responsive, and reversibly changes to enable repeated use. The light-driven actuator element includes a crystal of diarylethene compound which changes shape upon photoisomerization (e.g., the compound of Structural Formula (I) below, where R1 represents a hydrogen atom or methyl group and R2 represents a methyl group). The element can be a rod-shaped or plate-like microcrystal having a size on the order of micrometer. The element bends (or contracts) on irradiation with ultraviolet light and expands to return to the original size on irradiation with visible light.