Disclosed in the present specification are a digital device and a speech to text conversion processing method thereof. The digital device and the speech to text conversion processing method thereof according to the present invention may comprise the steps of: activating a text input field; checking the attribute of the text input field; receiving a request for a speech to text (STT) conversion processing with respect to data to be inputted in the text input field; determining whether or not the attribute type of the text input field is a security attribute (sensitive attribute); and as a determination result, if the attribute type of the text input field is a security attribute, blocking the speech to text conversion processing.