positive contact 15 a the battery t contact 15 b and the battery negative u2212 contact 15 c are electrically connected to the control substrate 13 the secondary battery 12 is protected by the protection apparatus 14 so that it electrically shuts off the secondary battery 12 from an excessive current when the excessive current flows the circuit blocks off the control substrate 13 when an excessive charge voltage is impressed and a battery voltage of the secondary battery 12 declines exceedingly and thereby protects the secondary battery 12 by allowing the thermistor 18 on the control substrate 13 to output an internal temperature of the battery pack 10 as a resistance a state of the secondary battery 12 can be determined with the configuration stated above when the battery pack 10 is normally inserted into the battery compartment 20 the concave portion 16 of the battery pack 10 is engaged with an engagement portion 25 of the battery compartment 20 while the battery pack 10 is being inserted one side of the protrusion 17 which is provided in a part of the concave portion 16 and each side of which is reinforced by the reinforcement portion 18 a left side in fig5 a and 5b abuts against the engagement lever 22 that is a constituent element of the engagement member the engagement lever 22 is tapered on a right side as shown in fig5 a and constituted to be movable forward and backward relative to the battery compartment 20 by the engagement spring 26 therefore the battery pack 10 can overpass the tapered portion of the engagement lever 22 and thereby can be smoothly moved in the insertion direction while the.