An optical measuring device comprises a plane mirror (3) having a center opening part functioning as a light entrance window or a light source mounting part (5) and an observation window (6') enabling the measurement by a light detector (6) and an integrating hemisphere (2) having the center of the radius of curvature in the center opening part of the plane mirror (3) and of which the inner wall surface functions as a light diverging and reflecting surface (1). An integrating space is formed between the plane mirror (3) and the integrating hemisphere (2). ©KIPO&WIPO 2009