A balance device (30, 66, 78, 140, 154, 156, 158, 168, 170, 202, 224, 302, 308, 330) for an internal combustion engine, comprising: a crankshaft (16, 178, 204, 226) that rotates with a CS main shaft (22, 232) as a rotating shaft; and a balance shaft (40, 80, 180, 198, 220, 224) that rotates with a BS axial shaft (44, 248) parallel with the CS main shaft (22, 232) as a rotating shaft, wherein the crankshaft includes a CS eccentric weight (24, 182, 208, 230) that makes a center of gravity of the crankshaft eccentric from a center of the CS main shaft, and the balance shaft (48, 184, 200, 210, 222, 246) includes a BS eccentric weight that makes a center of gravity of the balance shaft eccentric from a center of the BS axial shaft, the balance device further comprising: a connection rod (36, 256, 314) that connects a CS connected point provided on the crankshaft at a position deviated from the center of the CS main shaft, and a BS connected point provided on the balance shaft at a position deviated from the center of the BS axial shaft; a CS connection mechanism that enables relative rotation of the crankshaft and the connection rod with the CS connected point as a center of rotation; a BS connection mechanism that enables relative rotation of the balance shaft and the connection rod with the BS connected point as a center of rotation; and a guide section (54, 68, 82, 278, 324) that guides a motion of the connection rod so that the balance shaft rotates in an opposite direction to a rotation direction of the crankshaft, wherein said balance device is characterized in that said guide section (54, 68, 82, 278, 324) achieves the guide by sliding with the connection rod (36, 256, 314) or a slide portion (52,274) which the connection rod comprises. a crankshaft (16, 178, 204, 226) that rotates with a CS main shaft (22, 232) as a rotating shaft; and a balance shaft (40, 80, 180, 198, 220, 224) that rotates with a BS axial shaft (44, 248) parallel with the CS main shaft (22, 232) as a rotating shaft, wherein the crankshaft includes a CS eccentric weight (24, 182, 208, 230) that makes a center of gravity of the crankshaft eccentric from a center of the CS main shaft, and the balance shaft (48, 184, 200, 210, 222, 246) includes a BS eccentric weight that makes a center of gravity of the balance shaft eccentric from a center of the BS axial shaft, the balance device further comprising: a connection rod (36, 256, 314) that connects a CS connected point provided on the crankshaft at a position deviated from the center of the CS main shaft, and a BS connected point provided on the balance shaft at a position deviated from the center of the BS axial shaft; a CS connection mechanism that enables relative rotation of the crankshaft and the connection rod with the CS connected point as a center of rotation; a BS connection mechanism that enables relative rotation of the balance shaft and the connection rod with the BS connected point as a center of rotation; and a guide section (54, 68, 82, 278, 324) that guides a motion of the connection rod so that the balance shaft rotates in an opposite direction to a rotation direction of the crankshaft, wherein said balance device is characterized in that said guide section (54, 68, 82, 278, 324) achieves the guide by sliding with the connection rod (36, 256, 314) or a slide portion (52,274) which the connection rod comprises. a connection rod (36, 256, 314) that connects a CS connected point provided on the crankshaft at a position deviated from the center of the CS main shaft, and a BS connected point provided on the balance shaft at a position deviated from the center of the BS axial shaft; a CS connection mechanism that enables relative rotation of the crankshaft and the connection rod with the CS connected point as a center of rotation; a BS connection mechanism that enables relative rotation of the balance shaft and the connection rod with the BS connected point as a center of rotation; and a guide section (54, 68, 82, 278, 324) that guides a motion of the connection rod so that the balance shaft rotates in an opposite direction to a rotation direction of the crankshaft, wherein said balance device is characterized in that said guide section (54, 68, 82, 278, 324) achieves the guide by sliding with the connection rod (36, 256, 314) or a slide portion (52,274) which the connection rod comprises.