An exchangeable cartridge for a dental handpiece includes first dust-proofing members for preventing foreign matter from being intruded into an upper bearing and second dust-proofing members for preventing foreign matter from being intruded into a lower bearing. The first dust-proofing members have an upper rotational partitioning member and an upper fixed partitioning member. The upper rotational partitioning member has a protrusion provided above the upper bearing and protruding radially outwardly. The upper fixed partitioning member has a radially inwardly protruding portion lying adjacent and parallel to the protrusion of the upper rotational partitioning member to define a first interstice leading to the upper bearing. The second dust-proofing members have a lower rotational partitioning member and a lower fixed partitioning member. The lower rotational partitioning member has a protrusion provided below the lower bearing and protruding radially outwardly. The lower fixed partitioning member has a radially inwardly protruding portion lying adjacent and parallel to the protrusion of the lower rotational partitioning member to define a second interstice leading to the lower bearing.