An instrument (1,2,3,4,5,6,6',7,8) comprising a support member having a lateral surface, and a contact force sensor device that is integrated in said support member, said contact force sensor device including: - a gas-inflatable balloon arranged to switch between a deflated state, and an inflated state at an inflation pressure (Po) and arranged to protrude from said lateral surface of said support member when in said inflated state, said instrument comprising: - a feed duct arranged to feed a gas to said gas-inflatable balloon through a connection member engaged by an entrance portion of said gas-inflatable balloon; - an inflation/deflation valve assembly arranged to selectively connect said gas-inflatable balloon with a gas source or with a gas-discharge vent, respectively, through said feed duct; - a detector (41,42,43) configured to output a detection signal (51,52,53) responsive to a contact force-related value related to a contact force acting on said gas-inflatable balloon when said gas-inflatable balloon is in said inflated state and is engaged in a contact with a wall of a body outside of said support member; - a processing unit configured to: - receive an inflate input signal from a user; - upon receiving said inflate input signal, cause said inflation/deflation valve assembly to inflate said balloon to said inflated state; - receive said detection signal (51,52,53) and compute a contact force signal responsive to said detection signal (51,52,53) according to a predetermined function; wherein said function is a relationship between said contact force and said force-related value selected from the group comprised of: - said contact pressure; - a deformation value (x,A) of said gas-inflatable balloon; - a modification of a stretch condition of said membrane, said force-related value generated when said gas-inflatable balloon is in contact with said wall, - receive a deflate input signal from said user; - upon receiving said deflate input signal, deflate said gas-inflatable balloon to said deflated state, - a contact force-value notification device configured to receive said contact force signal from said processing unit and to notify to a user said contact force signal responsive to said contact force. - a gas-inflatable balloon arranged to switch between a deflated state, and an inflated state at an inflation pressure (Po) and arranged to protrude from said lateral surface of said support member when in said inflated state, - a feed duct arranged to feed a gas to said gas-inflatable balloon through a connection member engaged by an entrance portion of said gas-inflatable balloon; - an inflation/deflation valve assembly arranged to selectively connect said gas-inflatable balloon with a gas source or with a gas-discharge vent, respectively, through said feed duct; - a detector (41,42,43) configured to output a detection signal (51,52,53) responsive to a contact force-related value related to a contact force acting on said gas-inflatable balloon when said gas-inflatable balloon is in said inflated state and is engaged in a contact with a wall of a body outside of said support member; - a processing unit configured to: - receive an inflate input signal from a user; - upon receiving said inflate input signal, cause said inflation/deflation valve assembly to inflate said balloon to said inflated state; - receive said detection signal (51,52,53) and compute a contact force signal responsive to said detection signal (51,52,53) according to a predetermined function; wherein said function is a relationship between said contact force and said force-related value selected from the group comprised of: - said contact pressure; - a deformation value (x,A) of said gas-inflatable balloon; - a modification of a stretch condition of said membrane, said force-related value generated when said gas-inflatable balloon is in contact with said wall, - receive a deflate input signal from said user; - upon receiving said deflate input signal, deflate said gas-inflatable balloon to said deflated state, - receive an inflate input signal from a user; - upon receiving said inflate input signal, cause said inflation/deflation valve assembly to inflate said balloon to said inflated state; - receive said detection signal (51,52,53) and compute a contact force signal responsive to said detection signal (51,52,53) according to a predetermined function; wherein said function is a relationship between said contact force and said force-related value selected from the group comprised of: - said contact pressure; - a deformation value (x,A) of said gas-inflatable balloon; - a modification of a stretch condition of said membrane, said force-related value generated when said gas-inflatable balloon is in contact with said wall, - said contact pressure; - a deformation value (x,A) of said gas-inflatable balloon; - a modification of a stretch condition of said membrane, - receive a deflate input signal from said user; - upon receiving said deflate input signal, deflate said gas-inflatable balloon to said deflated state, - a contact force-value notification device configured to receive said contact force signal from said processing unit and to notify to a user said contact force signal responsive to said contact force.