An information input device includes a detection portion, a processor, and a memory. The detection portion is configured to detect a position of a writing portion being in contact with or close to the detection portion. The memory is configured to store computer-readable instructions. The computer-readable instructions, when executed by the processor, cause the information input device to perform processes that include acquiring position information at a predetermined time interval, setting, as first position information, information indicating one of positions indicated by the acquired position information, determining whether a distance between a position indicated by the set first position information and a position indicated by second position information is less than a threshold value, and storing, as information configuring trajectory information, the second position information in a storage portion in response to determining that the distance is not less than the threshold value.