PURPOSE: To reduce the size of a Porro prism by dividing the Porro prism into two, arranging a visual field frame at the division part, and forming the incidence surface of an incidence-side prism into a telecentric lens.

CONSTITUTION: The Porro prism is composed of a 1st prism 14 and a 2nd prism 15 which have two reflecting surfaces whose inward normals cross each other at about 120°, and arranged on an ocular side. The visual field frame 3 is arranged between the 1st prism 14 and 2nd prism 15, the 1st prism 14 is based upon a similar prism corresponding to the prism obtained by rotating the 2nd prism 15 by 180°, and the incidence surface side is made into the telecentric lens. An image formation plane is only formed at the position of the visual frame 3 as the function of the 1st prism 14 and subject luminous flux need not be guided to the frame part of the visual field frame 3, so the frame of the 1st prism is reducible in size correspondingly. Consequently, this finder can be made more compact than conventional one.