In this paper, we would like to introduce an in-line MTF (Modulation Transfer Function) measuring system which is compatible with the automated assembly process line of lens-modules in smartphone cameras. This in-line optical inspection system consists of a resolution chart module, Dual Cono-Scope Telecentric Lenses, imaging lenses, and a single detector. Unlike conventional measuring devices with many cameras that are more commonly used in the industry, this device can evaluate the MTF performance without reversing the lens module in an upside down position by applying a reverse projection method. So, it is possible to measure MTF for the full-fields of the lens module from any arbitrary desired positions, as well as the designated positions by using a single camera. This makes it compatible with the equipment of the automated production process line for lens modules. We will expect that the lens module production line will be diversified and fully automated through the application of this in-line optical inspection system.