Extension/contraction mechanism

An extension/contraction mechanism comprising a telescopic extension/contraction part, wherein

• the extension/contraction mechanism comprises:
• a first drive source connected to a screw shaft in such a way that it can transmit a drive force;
• a first belt holder that accommodates a second belt in such a way that the second belt can be sent out to the screw shaft or the second belt can be wound-up from the screw shaft;
• a second belt holder that accommodates a first belt in such a way that the first belt can be sent out to the screw shaft or the first belt can be wound-up from the screw shaft;
• and
• a first belt holder drive part and a second belt holder drive part, and
• wherein
• the extension/contraction part is extended when the screw shaft rotates in one direction and sends out the first belt and the second belt so that the first belt and the second belt are spirally wound in a state in which they are engaged with each other, and is contracted when the screw shaft rotates in the other direction and draws in the first belt and the second belt so that the state in which the first belt and the second belt are engaged with each other and wound is loosened,
• the first belt holder drive part rotates the first belt holder independently of the rotation of the screw shaft, and
• the second belt holder drive part rotates the second belt holder independently of the rotation of the screw shaft.