A rubber sheet member joining device, comprising: a pair of gripping parts (3, 4) for gripping, respectively, ranges in proximity to end surfaces (13a, 13b) of rubber sheet members to be joined, the rubber sheet members being unvulcanized; a drive unit that moves at least one of the pair of gripping parts (3, 4) in a direction approaching and separating from each other; and a control unit for controlling operation of the pair of gripping parts (3, 4) and operation of the drive unit, the rubber sheet member joining device being configured such that: at least one opposing surface (3a, 4a) of the pair of gripping parts (3, 4) comprises a contact member with a contact surface projecting towards another opposing surface (3a, 4a) of the pair of gripping parts (3, 4); when the pair of gripping parts (3, 4) are in close proximity to each other, the contact member is in a state of being sandwiched between the opposing surfaces (3a, 4a), and movement of the pair of gripping parts (3, 4) in proximity to each other is stopped; the ranges in proximity to the rubber sheet members are gripped, respectively, in a state in which the end surfaces (13a, 13b) project from the one opposing surface (3a, 4a) toward the other opposing surface (3a, 4a) of the pair of gripping parts (3, 4), respectively; and a total end surface projection amount (d) of the end surfaces (13a, 13b) from the opposing surfaces (3a, 4a), respectively, is set to be larger by a predetermined length than a separation distance between the opposing surfaces (3a, 4a) when the contact member is in a state of being sandwiched between the opposing surfaces (3a, 4a) and movement in proximity to each other is stopped, wherein the rubber sheet member joining device further comprises an adjustment mechanism (6a, 6b) for adjusting a contact surface projection amount (c1, c2) of the contact surface of the contact member that is gripped by the pair of gripping parts (3, 4), respectively, from the opposing surface (3a, 4a) of the pair of gripping parts (3, 4). a pair of gripping parts (3, 4) for gripping, respectively, ranges in proximity to end surfaces (13a, 13b) of rubber sheet members to be joined, the rubber sheet members being unvulcanized; a drive unit that moves at least one of the pair of gripping parts (3, 4) in a direction approaching and separating from each other; and a control unit for controlling operation of the pair of gripping parts (3, 4) and operation of the drive unit, the rubber sheet member joining device being configured such that: at least one opposing surface (3a, 4a) of the pair of gripping parts (3, 4) comprises a contact member with a contact surface projecting towards another opposing surface (3a, 4a) of the pair of gripping parts (3, 4); when the pair of gripping parts (3, 4) are in close proximity to each other, the contact member is in a state of being sandwiched between the opposing surfaces (3a, 4a), and movement of the pair of gripping parts (3, 4) in proximity to each other is stopped; the ranges in proximity to the rubber sheet members are gripped, respectively, in a state in which the end surfaces (13a, 13b) project from the one opposing surface (3a, 4a) toward the other opposing surface (3a, 4a) of the pair of gripping parts (3, 4), respectively; and a total end surface projection amount (d) of the end surfaces (13a, 13b) from the opposing surfaces (3a, 4a), respectively, is set to be larger by a predetermined length than a separation distance between the opposing surfaces (3a, 4a) when the contact member is in a state of being sandwiched between the opposing surfaces (3a, 4a) and movement in proximity to each other is stopped, wherein the rubber sheet member joining device further comprises an adjustment mechanism (6a, 6b) for adjusting a contact surface projection amount (c1, c2) of the contact surface of the contact member that is gripped by the pair of gripping parts (3, 4), respectively, from the opposing surface (3a, 4a) of the pair of gripping parts (3, 4). at least one opposing surface (3a, 4a) of the pair of gripping parts (3, 4) comprises a contact member with a contact surface projecting towards another opposing surface (3a, 4a) of the pair of gripping parts (3, 4); when the pair of gripping parts (3, 4) are in close proximity to each other, the contact member is in a state of being sandwiched between the opposing surfaces (3a, 4a), and movement of the pair of gripping parts (3, 4) in proximity to each other is stopped; the ranges in proximity to the rubber sheet members are gripped, respectively, in a state in which the end surfaces (13a, 13b) project from the one opposing surface (3a, 4a) toward the other opposing surface (3a, 4a) of the pair of gripping parts (3, 4), respectively; and a total end surface projection amount (d) of the end surfaces (13a, 13b) from the opposing surfaces (3a, 4a), respectively, is set to be larger by a predetermined length than a separation distance between the opposing surfaces (3a, 4a) when the contact member is in a state of being sandwiched between the opposing surfaces (3a, 4a) and movement in proximity to each other is stopped, wherein the rubber sheet member joining device further comprises an adjustment mechanism (6a, 6b) for adjusting a contact surface projection amount (c1, c2) of the contact surface of the contact member that is gripped by the pair of gripping parts (3, 4), respectively, from the opposing surface (3a, 4a) of the pair of gripping parts (3, 4).