To provide a photocatalyst device capable of improving the degree of freedom in design thereof.SOLUTION: A photocatalyst device according to an embodiment includes: a light source that emits light having a predetermined wavelength； a substrate that is provided on the light emission side of the light source and transmits the light； a photocatalyst portion that is provided on the surface of the substrate opposite to the light source side and includes a photocatalyst； and at least one light transmitting portion that is provided in the photocatalyst portion and penetrates in a thickness direction of the photocatalyst portion.SELECTED DRAWING: Figure 4【課題】光触媒装置の設計の自由度を向上させることができる光触媒装置を提供することである。【解決手段】実施形態に係る光触媒装置は、所定の波長を有する光を出射する光源と；前記光源の、前記光の出射側に設けられ、前記光を透過させる基体と；前記基体の、前記光源側とは反対側の面に設けられ、光触媒を含む光触媒部と；前記光触媒部に設けられ、前記光触媒部の厚み方向を貫通する少なくとも１つの透光部と；を具備している。【選択図】図４
