The present invention relates to a transmission interface device capable of calibrating the transmission frequency automatically, which comprises a clock generating unit, a data transmission unit, and a control unit. The clock generating unit is used for generating an operating clock, which determines a transmission frequency. The data transmission unit is used for connecting to a host and transmitting a plurality of data to the host or receiving the plurality of data from the host according to the operating clock. When the host or the data transmission unit detects transmission errors in the plurality of data, the host or the data transmission unit generates an error handling. The control unit generates an adjusting signal according to the error handling and transmits the adjusting signal to the clock generating unit for adjusting the transmission frequency of the operating clock.