A microreactor for photoreactions includes a housing upper part, a lid plate made of a material that allows transmission of light, a flow path plate made of a material that suppresses light reflection and has a high thermal conductivity, and a housing lower part. Light is applied through a window of the housing upper part and the lid plate to a flow path of the flow path plate. The lid plate made of the material that allows transmission of light and the flow path plate made of the material that suppresses light reflection and has a high thermal conductivity are welded each other to form an integrated body.