In this small-diameter drill bit, two cutting blades (7) having main cutting blades (7a), of which a difference between lengths (W) are 0.04 mm or less, are formed on a tip of a double-margin drill bit body (1) having a diameter of 2 mm or less and a margin length/diameter ratio of 3 or more. Two tip flank faces (5) are formed such that a first extension line (N1) extending from a linear first intersecting ridgeline (M1) between a first tip flank face (5a) and a second tip flank face (5b) of one of the flank faces to the linear first intersecting ridgeline (M1) of the other flank face is located on a side in the drill bit rotation direction (T) with respect to the other linear first intersecting ridgeline (M1). A distance (d1) between the first extension line and the linear first intersecting ridgeline is in a range of 0.04 mm-0.08 mm. A second extension line (N2) extending from a linear second intersecting ridgeline (M2) between the second tip flank face (5b) and a thinning face (8a) of the one flank face to the linear second intersecting ridgeline (M2) of the other flank face is located in a straight line with the other linear second intersecting ridgeline (M2) or located on the side in the drill bit rotation direction (T) with respect to the other linear second intersecting ridgeline (M2). A distance (d2) between the second extension line and the linear second intersecting ridgeline is in a range of 0.08 mm or less.