The present invention relates to a needle-guiding device (2) for a specified drilling resistance measurement unit, a drilling resistance measurement unit itself for investigating the nature of wood, and to a method for investigating the nature of wood. The needle-guiding device (2) for the drilling resistance measurement unit is designed to guide the drill needle (1) and to be operatively coupled to a drive of the drilling resistance measurement unit. The needle-guiding device (2) has a supporting device and a needle holder (4). The needle holder (4) has a drill chuck which is designed to receive the specified drill needle (1), and the supporting device extends in the longitudinal direction of the specified drill needle (1). According to the invention, the supporting device comprises at least one scissor-type extending grid device (8) having a scissor-type extending grid (8′) consisting of bars (81) or has a drive device having two interacting force transmission elements which are arranged parallel next to each other.