An apparatus for detecting an erroneously inserted empty bobbin is disposed on a spinning frame which is provided with an automatic doffing and donning apparatus and a conveyor having empty bobbin supporting pegs mounted thereon. The detecting apparatus photoelectrically or electromechanically detects whether or not an empty bobbin is correctly inserted onto the corresponding empty bobbin supporting peg based on the fact that an incorrectly inserted bobbin inclines backwards and projects upwards. When the incorrectly inserted bobbin is detected, an alarm is actuated in order to notify an operator in charge of the spinning frame of the same.