A substrate processing apparatus includes a base portion 1541 that is disposed in a manner of being adjacent to a chamber; a hand 155 that holds a substrate S; an arm 1542 that is attached to the base portion 1541, supports the hand, and moves the hand forward and rearward by horizontally moving the hand with respect to the base portion; and a cover portion 156 that accommodates the hand in an internal space. The cover portion has a cover main body 1561 forming the internal space and an extending member 1562 having a hollow structure which penetrates the cover portion in a horizontal direction and of which one end serves as an opening 1562a and being engaged with the cover main body in a state of being movable in the horizontal direction while the opening communicates with the internal space.