Network protocol reverse engineering is the basis for many security applications. A common class of protocol reverse engineering methods is based on the analysis of network message traces. After performing message field identification by segmenting messages into multiple fields, a key task is to infer the semantics of the fields. One of the limitations of existing field semantics inference methods is that they usually infer semantics for only a few fields and often require a lot of manual effort. In this paper, we propose an automated field semantics inference method for binary protocol reverse engineering (FSIBP). FSIBP aims to automatically learn semantics inference knowledge from known protocols and use it to infer the semantics of any field of an unknown protocol. To achieve this goal, we design a feature extraction method that can extract features of the field itself and of the field context. We also propose a semantic category aggregation method that abstracts the fine-grained semantics of all fields of known protocols into aggregated semantic categories. Moreover, we make FSIBP infer semantics based on the similarity of fields to semantic categories. The above design enables FSIBP to utilize the semantic knowledge of all fields of known protocols and infer the semantics of any fields of unknown protocols. The whole process of FSIBP does not require any expert knowledge or manual parameter setting. We conduct extensive experiments to demonstrate the effectiveness of FSIBP. Moreover, we find a utility for FSIBP besides field semantics inference, its output can help to detect the mis-segmented fields generated during the message field identification.