PROBLEM TO BE SOLVED: To accurately determine whether or not liquid is leaked around a gasket.SOLUTION: A liquid leakage inspection device 2 inspects liquid leakage of a prefilled syringe 1 which is provided with a cylindrical syringe body 3 filled up with liquid and a gasket 4 which is inserted from a back part of the syringe body 3 and has a circular groove 4a formed on an outer circumference surface. The device irradiates electromagnetic wave comprising terahertz waves W, transmits a focus of the electromagnetic wave through the syringe body to be formed inside the groove 4a of the gasket, moves the focus of the electromagnetic wave all over the circumference of the groove of the gasket, detects reflection intensity of the electromagnetic wave reflected inside the groove of the gasket, and determines that liquid leakage has occurred to the gasket when the reflection intensity of the electromagnetic wave is below a prescribed threshold. Also, the device determines whether or not liquid leakage has occurred to a cap by forming a focus of the electromagnetic wave between a needle attachment part formed at the end of the syringe and the cap.
