The present invention provides a packet stream receiving apparatus, comprising a packet separation section that extracts a presentation time from a packet, a discontinuity detection section that detects a discontinuity of the packet, a storage buffer that stores decoded frames after the discontinuity has been detected, and a presentation time comparison section that calculates a number of lost frames based on the actual number of frames received from a discontinuity point in which the discontinuity was detected until the presentation time is obtained in the case where the storage buffer has stored the decoded frames. By accurately comprehending the number of lost frames caused by packet losses, outputs without timing mismatch are enabled.