Provided are an objective optical system capable of narrowband light observation and white light observation at the same time using a highly versatile imaging element despite being a small-sized optical system, and an endoscope device provided with the same. An objective optical system 1 has a lens group 2 for forming an image of an object and an light path splitting element 3 disposed on the image side of the lens group 2, the light path splitting element 3 having an light path splitting surface for forming a first light path and a second light path, the first light path being formed on an extension line of the second light path, the second light path being formed so as to intersect with the first light path, an optical image I1 in the first light path and an optical image I2 in the second light path being formed on the same plane, a reflecting surface being positioned in the second light path, a predetermined optical surface being positioned in only one of the first light path and the second light path, the wavelength region of light transmitted through the predetermined optical surface or the wavelength region of light reflected by the predetermined optical surface being restricted, and the restricted wavelength region being narrower than the wavelength region of light progressing in the other light path.L'invention concerne un système optique d'objectif capable d'observation de lumière à bande étroite et d'observation de lumière blanche en même temps à l'aide d'un élément d'imagerie extrêmement polyvalent malgré un système optique de petite taille ； et un dispositif d'endoscope le comprenant. Le système optique d'objectif 1 comprend un groupe de lentilles 2 qui forment une image d'un objet et un élément diviseur de trajet lumineux 3 situé côté image du groupe de lentilles 2, ledit système étant caractérisé en ce que l'élément diviseur de trajet lumineux comporte une surface qui divise le trajet lumineux de façon à former un premier trajet lumineux et un second t
