Abstract: There is described a data-imprinting optical system for use with a camera which is composed of a single meniscus lens having a positive refracting power and a brightness aperture, which can be applied to a low-cost unsophisticated camera of manual advance type by satisfying predetermined conditional equations, and which enables miniaturization of and space-saving in a camera. Specifically, the data-imprinting optical system includes a single positive meniscus lens and a brightness aperture disposed on the part of a data display member. The positive meniscus lens is a plastic lens having an aspherical concave surface on the part thereof facing the data display member. An image of display information appearing on the data display member is projected on a film surface.