In order to provide a connection device whereby an operation for connecting and locking a device connector to a container connector and an operation for unlocking and disconnecting the same can easily be performed, a connection device 10 is provided with a syringe connector 100, a container connector 20, a second arm part 232, and a locking recess 67. The syringe connector 100 is provided with a head sleeve 180, a needle 170, a needle seal 200, and an outer body main body 11 for forming a liquid flow path communicated with the inside of a syringe 6. The container connector 20 is provided with a needle part 50, a liquid flow path formation part L3, and a container seal 70. The second arm part 232 and the locking recess 67 are engaged in a state in which the needle 170 penetrates through the needle seal 200 and the container seal 70 and is communicated with the liquid flow path formation part L3.
