To provide an automatic document feeder enabling quick and easy maintenance operation for a separation member and an elastic member.

This ADF includes an inner guide 19 for guiding a document, mutually opposed rollers 37 disposed on the inner guide 19 for separating one by one the sheets of the document, and a spring for pressing the opposed rollers 37. The ADF further includes a unit frame 81 which supports the opposed rollers 37 and the spring and is constituted detachably from the inner guide 19. The unit frame 81 has an adjusting mechanism for adjusting the pressing force of the spring which presses the opposed rollers 37. The unit frame 81 has an adjustment cover 92 detachably installed for protecting the adjusting mechanism. The adjusting mechanism is formed in such a manner that the adjusting portion for adjusting the pressing force is exposed when the adjustment cover 92 is removed.