To protect a monitoring device from discriminating the variation of a monitoring picture as abnormality when the change is caused by the movement of a registered picture by registering pictures which are predicted to move in a background picture.

A background picture from a camera 1 is converted into digital data by means of an A/D converter 2 and written in a background picture memory 10 and a picture memory 3 and pictures which are predicted to move are set by means of a setting means 6, extracted by means of a picture extracting section 7, and registered in a registered-picture memory 8. The picture supplied from the A/D converter 2 from one minute to the next are written in a monitored-picture memory 11 and the correlation between the pictures from the memories 10 and 11 are calculated by means of a correlation calculating section 12. When a difference discriminating section 14 discriminates a difference between the pictures, a correlation calculating section 16 calculates the correlations between the pictures from the memories 11 and 8 and an abnormality discriminating section 17 discriminates the presence of abnormality, and then, a clock section 18 counts time. When the difference continuously exist even after a required period of time counted by means of a time discriminating section 19 has elapsed, the picture which is stored in an abnormal-picture memory after the picture is transferred to the memory from the memory 11 is read out from the memory and outputted from an output section 21.