Pressing jig and pressing device thereof

A pressing jig includes a support plate, a sliding rail, a base and a pressing device. The sliding rail is disposed on the support plate. The pressing device includes a sliding base, an extension plate, a connection plate, a first pressing head assembly, a second pressing head assembly and a third pressing head assembly. The sliding base is vertical-movably disposed on the sliding rail. The extension plate is connected with the sliding base and extended from the sliding base towards the base. The connection plate is connected with the extension plate. The first pressing head assembly, the second pressing head assembly and the third pressing head assembly are disposed on the connection plate and respectively having a first height, a second height and a third height. The first height is greater than the second height, and the second height is greater than the third height. When the sliding base is moved towards the base, the first pressing head assembly, the second pressing head assembly and the third pressing