Abstract: Disclosed is a floorboard to provide simplified assembly of flooring panels without damage and achieve enhanced horizontal coupling force. The floorboard includes a tongue part provided at a first flooring panel and a recessed part provided at a second flooring panel. The tongue part includes a tongue protrusion, a tongue bottom portion, and a raised retaining portion protruding downward from the tongue bottom portion. The recessed part includes an upper lip caught by the tongue protrusion when the tongue part is inserted into the recessed part, a lower lip, a raised portion protruding upward from an end of the lower lip, and a guide wall defining an inner wall of the recessed part and having the same contour as an arc drawn by an end of the tongue protrusion as the tongue part introduced between the upper and lower lips is pivotally rotated.