A coordinate input apparatus in which a vibration which was input by a vibration input pen is detected by vibration sensors attached to a vibration propagating plate such as a transparent glass plate or the like and the coordinates of the position of the pen on the plate are detected. The apparatus includes an envelope output circuit to output envelope signals of detection signals of the sensors; a filter circuit for filtering the envelope signals; a gate signal output circuit for detecting a portion, exceeding a predetermined threshold value, of the envelope signal output from the filter circuit and for outputting a gate signal; a first detector for detecting the peak of the envelope signal output from the envelope output circuit and for detecting the envelope signal by using the peak as a reference; a second detector for detecting a phase signal of the detection signal by using the leading edge of the phase signal as a reference in the period of time during which the gate signal output from the gate signal is output circuit; and a calculating circuit to calculate the position coordinates of the input pen on the basis of the propagation time of the envelope signal detected by the first detector and the propagation time of the phase signal detected by the second detector.