PURPOSE: To detect the deteriorated state of a bubble memory device easily without stopping an operation by forming a conductor pattern for measuring an electric change in the lapes of time on the bubble memory chip on which a function gate or the like is formed and connecting the pattern to lead terminals so as to check an electric characteristic.

CONSTITUTION: A function gate such as a generator Ge or the like, lead patterns 3W8 and a monitor pattern 9 in the chip 1 are formed at the same time by etching selectively a conductor film coated on an LPE film. Further, the chip 1 completed by forming a bubble transfer path or the like is mounted on a chip mounting board so as to complete the entire device as a magnetic bubble memory device, then the monitor pattern 9 tends to receive the effect of water vapor or harmful gas immersed into the package of the device more than the function gate. Thus, in checking periodically the electrical characteristic of the monitor pattern 9 via the lead terminals led out of the package, the deterioration of the function gate is estimated.