A balance device for an internal combustion engine , comprising: a crankshaft that rotates with a CS main shaft as a rotating shaft; and a balance shaft that rotates with a BS axial shaft parallel with the CS main shaft as a rotating shaft, wherein the crankshaft includes a CS eccentric weight that makes a center of gravity of the crankshaft eccentric from a center of the CS main shaft, and the balance shaft 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 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 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 achieves the guide by sliding with the connection rod or a slide portion which the connection rod comprises. a crankshaft that rotates with a CS main shaft as a rotating shaft; and a balance shaft that rotates with a BS axial shaft parallel with the CS main shaft as a rotating shaft, wherein the crankshaft includes a CS eccentric weight that makes a center of gravity of the crankshaft eccentric from a center of the CS main shaft, and the balance shaft 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 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 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 achieves the guide by sliding with the connection rod or a slide portion which the connection rod comprises. a connection rod 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 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 achieves the guide by sliding with the connection rod or a slide portion which the connection rod comprises. <EOS>