An automatic hold time fixing circuit unit includes a first switch having first and second ends connected to data input and output ports. An input end of a memory element is connected to the second end of the first switch. A second switch includes a first end connected to an output end of the memory element and a second end connected to the data output port. A control circuit includes first and second output terminals and first and second input terminals. The first and second output terminals are connected to control ends of the first and second switches. The first and second input terminals allow input of two clocks to the control circuit for controlling connection or disconnection of the first and second switches. The data stored in the memory element can be utilized to fix a hold time of the data, so that correct data can be obtained at the data output port.