A navigation device may include a GNSS data editing part, an attitude angle calculating part, and a speed calculating part. The GNSS data editing part may generate GNSS attitude angle estimation data and GNSS speed estimation data by using first GNSS data based on a GNSS signal received by a first antenna, and second GNSS data obtained at a shorter cycle than the first GNSS data based on a GNSS signal received by a second antenna. The attitude angle calculating part may estimate an integrated attitude angle based on the IMU angular velocity outputted from an Inertial Measurement Unit (IMU) and the GNSS attitude angle estimation data. The speed calculating part may estimate an integrated speed based on an IMU acceleration outputted from the IMU, the GNSS speed estimation data, and the integrated attitude angle.