A signal processing device comprising: a processor configured to execute a program; and a memory that stores the program configured to cause the processor to function as a detection unit that transmits a signal to one or more signal lines (36, 38) formed of a breakable material in such a manner that the signal passes through regions corresponding to one or more respective container portions of a package for containing articles, and detects seal breakage of each container portion on the basis of whether the transmitted signal returns via each region; wherein the detection unit detects seal breakage of a first container portion, in a case in which a first signal does not return via a first region when a predetermined delay time has elapsed since a transmission time of the first signal that is to pass through the first region corresponding to the first container portion; wherein the detection unit does not determine whether the first signal returns via the first region, once the detection unit detects the breakage of the seal of the first container portion; wherein the one or more signal lines (36, 38) are a plurality of branch lines that branch from a common line, and wherein the detection unit transmits the first signal to a first branch line that extends through the first region corresponding to the first container portion, and determines whether the first signal returns from the common line, characterised in that the detection unit does not determine whether the first signal returns via the first region by skipping the following steps of a seal breakage detecting process executed by the detection unit: - transmitting the first signal to the first branch line, - waiting for predetermined delay time, - determining whether the first signal has returned, - updating a seal breakage flag of the first container portion, and - recording seal breakage time, once the detection unit detects the breakage of the seal of the first container portion. a processor configured to execute a program; and a memory that stores the program configured to cause the processor to function as a detection unit that transmits a signal to one or more signal lines (36, 38) formed of a breakable material in such a manner that the signal passes through regions corresponding to one or more respective container portions of a package for containing articles, and detects seal breakage of each container portion on the basis of whether the transmitted signal returns via each region; wherein the detection unit detects seal breakage of a first container portion, in a case in which a first signal does not return via a first region when a predetermined delay time has elapsed since a transmission time of the first signal that is to pass through the first region corresponding to the first container portion; wherein the detection unit does not determine whether the first signal returns via the first region, once the detection unit detects the breakage of the seal of the first container portion; wherein the one or more signal lines (36, 38) are a plurality of branch lines that branch from a common line, and wherein the detection unit transmits the first signal to a first branch line that extends through the first region corresponding to the first container portion, and determines whether the first signal returns from the common line, characterised in that the detection unit does not determine whether the first signal returns via the first region by skipping the following steps of a seal breakage detecting process executed by the detection unit: - transmitting the first signal to the first branch line, - waiting for predetermined delay time, - determining whether the first signal has returned, - updating a seal breakage flag of the first container portion, and - recording seal breakage time, - transmitting the first signal to the first branch line, - waiting for predetermined delay time, - determining whether the first signal has returned, - updating a seal breakage flag of the first container portion, and - recording seal breakage time, once the detection unit detects the breakage of the seal of the first container portion.