The invention provides a sealing device. The sealing device comprises a mounting frame, and a worktable erected on the mounting frame; a lower fixing plate and an upper pressing plate matched with sealing are arranged on the worktable; and a sealing heating device is arranged on the lower fixing plate. A plastic bag is put between the lower fixing plate and the upper pressing plate during working, and is sealed through heating of the sealing heating device. The mounting frame is provided with a pushing device fixedly connected with the upper pressing plate; and the worktable is provided with an induction device for detecting passing of the plastic bag. The sealing device further comprises a control device connected with the induction device and used for controlling the pushing device to work after inducing the plastic bag. The induction device is connected with the control device; after the plastic bag passes through the induction device, the induction device sends a signal to the control device; and the control device automatically controls the pushing device to perform action, so that the driving of sealing actions of the upper pressing plate and the lower fixing plate is realized, the automatic sealing of the plastic bag is realized, and the working convenience of the sealing machine is improved. The invention further provides a plastic bag sealing machine.