A front-lit detector includes a collimator, an X-ray to visible light converter configured to convert X-rays to visible light after the X-rays pass through the collimator to irradiate the X-ray to visible light converter, a visible light to analog signal converter configured to cover the visible light into analog signals, a substrate on which the visible light to analog signal converter is placed, and an A/D converter configured to convert the analog signals into digital signals.
