PURPOSE: To provide an improve multistage optical can gate device to be used for obtaining a gate output signal having a large S/N ratio and a short continuing time.

CONSTITUTION: This device includes at least two optical car gates 69 and 83 including polarizers 71, 85 and activate-analyzers 75 and 89 or includes a pair of at least two polarizers 71, 85 sharing at least one common optical Kerr cell 73 and the analyzers 75 and 89. In addition, the device includes a means for making a gating pulse (pump pulse) and a signal pulse (prove pulse) asynchronously reach a second optical Kerr cell 87 (when at least two car gates are provided) or the common optical Kerr cell (when at least two pairs of the polarizer and the analyzer are arranged so as to share the common optical Kerr cell).