To provide a transmission monitor system of still picture, which is provided with an automatic monitoring function in accordance with a JPEG (color still picture encoding) system.

The still picture transmission monitor system is constituted of a counting means 209, an extending and controlling means 211 and an announcement control means 215. The counting means counts the data amount of received compression picture data. Compression picture data is the still picture. The data is provided with the data amount for the portion of one screen. The extending and controlling means detects the change amount of the counted data amount 115 and selectively generates an announcement instruction 212 based on the detected change amount and the previously set change amount. The announcement control means responds to the announcement instruction and drives a ringing means 225. A compression rate deciding table 214 sets a quantizing coefficient to be changed in accordance with a difference between the detecting change amount and the previously set change amount. Based on the difference, the extending and control part refers to the table and selectively decides a quantizing error to be changed.