PURPOSE: To provide an uninterruptible memory slip alarm detection circuit in which configuration is simplified and the scale reduction is realized.

CONSTITUTION: An S-R circuit 4 collates timewise positions of write signals C, D used to write transmission data of two systems to storage circuits 1, 2 and outputs a square signal L, then one comparator circuit being the S-R circuit 4 is enough. A register circuit 5 samples the square wave signal L by a read signal E to output a level amount M of the square wave signal L and a level change detection circuit 6 detects a prescribed change in the level amount M to be in error to obtain an alarm signal N.