To precisely grasp how a bat is being swung by a method wherein a measuring instrument comprising a spring and a spherical weight is incorporated into a cavity formed in a baseball bat to display the speed of the weight when it has reached a measuring point and to display how many time the weight has passed the measuring point.

A baseball bat 1 is divided into two parts and a groove 2 is formed in each parts, and sensors 3, 4 are arranged in each groove. The sensors are connected to measuring instruments 5, 6 by wires. An end of a spring 8, to the forward end of which a spherical weight 7 is attached, is fixed to the groove 2 at a location on the side of a grip of the bat 1. Thus, when the bat 1 is swung, the weight 7 is moved in the groove 2 toward the forward end of the bat 1 so as to be sensed by the sensors 3, 4. That is, the sensor 3 senses a point to which the weight 7 has moved, while the sensor 4 measures how many times the weight 7 has passed the point. As a result, if a reference of the power of swinging of the bat is set by means of the spring constant of the spring 8 and the location to which the weight 7 has moved, the sharpness of swinging can also be grasped.