A threaded shaft (52) for operating toggle joint (44) is driven for rotation by a first servomotor (46). A bevel gear (56) is mounted on the threaded shaft (52) for rotation relative to the threaded shaft (52). The bevel gear (56) is driven for rotation by a second servomotor (57). Bevel gears (60) each having a threaded bore are supported on a rear plate (42) are engaged with threaded sections (40A) of tie bars (40), respectively. Power is transmitted from the bevel gear (56) through power transmitting mechanisms (61) to the bevel gears (60). Each power transmitting mechanism (61) comprises bevel gears (62, 63) engaged with the bevel gears (56, 60), respectively, and a clutch (64) interposed between the bevel gears (62, 63). The clutches (64) are engaged and disengaged selectively to adjust the parallelism of a movable mold (36) with respect to a stationary mold (32).